The Screen is too dim or too bright ?  (See a dead screen? can be a dead PC as   seen here.)
The hot keys for laptops screens work in BIOS pages (even if HDD is removed), if this fails  the Screen is bad (or keyboard dead )
All screens made before magic year 2010 fail for bad CCFL  , dead, dim, flickering, yellow tinged, or wildly random functioning)
If BIOS screens fail, it sure is not software related and  is hardware failure.
I have a modern Desktop and mondern monitor and the PC can change the brightness via the modern edid chip in side the monitor (laptop style)
Do not condemn any screen for windows issues (vast) Use your BIOS screens first to prove the screen really is dim or failing.(Dell F2 screen)
That means do not let sleep mode (get stuck) or hibernate mode ,or windows screen saver fool you, use the BIOS screens first as your acid test.
The Desktop has and external monitor that can be tested on 2 PCs proving it is bad in minutes work. (it too is subject to the TIMER 2010 or less rule)
The Desktop monitor has front panel brightness buttons or for sure inside the  OSD menus, via its MENU button on the monitor. (OSD = on screen display)
On Laptops remove the main huge battery and if the screen goes brigher (you have a battery/dead or  charge problem only)
Go home
Page Menu:
  1. Desktop DIM (real ATX) DIM issues. (fixes and causes)?
  2. Laptops DIM (mobile PCs)?
  3. The laptop battery running PC or low the PC goes dim as seen here.
  4. Dead or UGLY LCD  screens?
  5. Dead monitors.?
  6. Examples?
  7. Use presentation mode, or the like methods, To prove out (what is the cause  of dim or black screens)
  8. Relic Monitors (2007 and older)
  9. Or those old relic Monitors with VACUUM  CRT's; really?"Cathode Ray Tubes?"
  10. PC freezing, and related to screens .

My BIOS screens work perfect and if it boot a Linux demo disk (try me) the screen works under free linux.
If BIOS works and Linux demo works then the cause is not hardware, see all causes below.
One more hardware cause is this:
In some rare cases the PC power systems can be week or  overloaded, or the laptops big battery is failing (remove it  and run on AC full time) See topic strip down here
RARE and Relic  CRT displays are now history as is phosphor burned and now dim forever or weak electron guns (e-beam weak) Cure is buy a new LCD monitor.
The Desktop monitors have an  INSIDE IT, sleep timer , (time based and is on by default seen from year 2000 to 2010 ) the cure is: turn that off please.

This section below is Windows failing (mostly):

I will not try to explain fully why sleep modes exist.  (wiki it?)
Windows did this to me?, List:
  • The sleep mode is turned on
  • Hibernate, see above link.
  • The kids were playing and turn on screen saver and picked black screen as the choice, hit any key and it exits to normal unless keyboard is failing, and mouse wiggling fails. (disable screen saver is the cure) google that.
  • Windows, Video GPU chip or card driver is missing dead or wrong, go to you OEM PC makers web site and the cure is get your correct driver matching YOUR PC and YOUR OS.
  • Windows is infected, with virus or malware.  (reload windows)
  • The desktop PC may have "Adaptive  brightness"  using the frame camara to dim the screen in a brightly lit room (put tape over  the camera to prove this or turn this feature off in windows.)
  • My Laptop BIOS lists this feature  'Built in ambient light sensor"  so turn it off.  on some PCs the BIOS may even dim it  for this or the battery below)
  • All Laptops have a low battery (main) detector  and dims the screen to save battery life (extends run time on battery) so turn this OFF.

Power settings Adjustments:
The Power ICON in the (CP) or Control panel , lets you see the many modes to flip on or off or the delay.   Turn them all off is the CURE (or just to prove this is it)
Rule 1: Do not expect power setting to work right if your DRIVERS are bad, wrong , corrupted or Missing. Sorry but drivers are first. SEE that here.
Again the drivers must not look like this, showing they are bad, this is first, wrong or missing drivers will cause sleep modes to fail. The cure is simple for bad drivers , get new and matching drivers.
Display screen problems are addressed and cured on this page.
Dead USB devices are covered here, and simple cures if your drivers are not bad.

    The Top cause are wrong drivers, or even caused by running the wrong OS, called by me the act of  slamming the PC.
    If your OEM does not support W10 -64bit on your PC and you ignored that fact, that is what I call slamming the PC and sure lots of things will fail sure. (self inflicted too)

     Examples: It's not a bug it is a FEATURE !

    Here is W10 , that is now stuck in  power saver mode...  on Modern Laptop. (Elitebook , HP)
    The test (and cause and cure ) is easy, remove the huge battery and if the screen goes bright the battery is bad, or not charges or the AC Pack is dead. (or turn off this feature if you don't like it)
     Photo 3:(running on battery only now)             (btw, running on A.C ONLY looks like this see the battery X, means missing or bad.)
    HP 8540w, dimmed now. (used photo shop(tm) to make it look bright, it's not at all)
    If shows 50% here,
    then Windows is Dimming it, for sure.  (one can set the % anywhere one wants at any time)
     I am clicking the battery icon here, to pop up the battery status screen.
    The Power controller runs in DC and AC modes.  (on battery or on AC) independently by default. The OS and BIOS do this to make the battery run longer.. (run time)

    FACTOID:   (even only 1 year old , if a main battery is abused, or as we say DEEP CYCLE way too often) they fail. and when failed, or worse shorted this confuses the H3LL out of the charge chip and the software behind it !
    Batteries love to fail, then you ignore that? and wonder why the screen dims?, it dims because the PC thinks (or may know ) the battery is bad or weak or discharging and goes to DIM mode.
    The Charging chip is not GOD, It can not know or understand all ways a battery or even one cell in a battery can fail,  after all each cell or all can be, open/shorted/weak/intermittent.  So do not trust it, learn to use your backup battery first.
    Only HUMANS can test a battery not some $1 chip. Sorry but that is a fact, and only YOU KNOW what run times you need , no other person nor any chip on earth knows your needs.
    The book that you did not read day one told you, run times decrease every day, you use the PC,  and increases the more you over use the battery, called, excess deep cycling it. (hint keep the AC pack plugged in to the WALL)
    That means it's really a battery issue, only.  (or AC power pack died)  but you can turn all that green stuff off at any time.
    If the battery is old and weak, as all are, old.  The battery will have poor run time.  (use DIM mode until you get a new battery would be best)
    The charge chip in the PC LT mother board can get confused if one more cells in the battery are shorted. (some even catch fire shorted)  When confused the displayed data can lie, for sure state of charge %
    No lie, in this mode the battery can run 2 times longer dimmed (in some cases with a fresh new battery)
     Batteries can fail in 2 years, time or even less. (keep the AC pack plugged in and avoid most of that battery stress and the DIM issues)
    The Battery lasts the longest if not cycled, keep the AC pack plugged in to reduce battery cycling (charge,discharge,charge, repeat is not good for the battery)
    Store batteries fully charged.
    Some PCs laptops have a battery load test or battery learn mode, it is a nice idea, but if the battery has odd problems, as many batteries just love to have , it will lie to you. (funny that, no?)
    What matters ONLY is how long it runs doing real  battery mode operations, (no AC line connected) only that matters, and in most cases only a new battery passes this test, the human test, using the PC as designed on battery power.
    Why wait, buy a $15 new battery, keep in 1/2 charged ,stored on  a shelf, and have it with you on vacation, because you will not find it , far from home on vacation will you? A whole whopping $15.

    PRESENTATION mode is very handy for 2+ reasons, (use this  as a test to learn how it works or to prove these feature are your problem or as a CURE)
     DLP projectors in a home theater,  using  Kiosk mode  or power point presentations to a large room of people
    If any chip in the PC (vast numbers of chips) goes to sleep when you don't want that or can not suffer the results of this, then turn them all off, but there are so many bits to flip in CP Power  settings. (ugh !)
    Reason #2,  Many PCs have bad drivers on many chips or just buggy and the maker of said chip flat refused to fix this !, then turn on presentation mode, forcing the PC not use that bug ridden mode. (hibernate is worse)
    Reason #3 use Your TV as a screen and the PC is say running Netflix movies? Run Presentation mode.
    OK here is the fix.

    If all this sleep/ hibernate modes drives you mad, or you want to use  your PC with any Projection systems or use the Laptop External Video to external display and not suffer pain? (VGA/DVI or HDMI)
    What can you do,? (for sure do not use the CP + Power options mode ADVANCED, to set like 20 bits there to get it like you want,  a real pain that is. CP = Control panel.
    Set all sleep to off
    Set all hibernate to off
    Set all wake on, chips , to enabled. (for sure enable USB wake)

    We can do this many ways, your actions.
    • Control panel, windows mobility center) click external display set it as you want, or need. (missing on w10 desktops)
    • On W7 up, we open the start button (or press the windows key) or go to start search , paste in "presentationsettings.exe"  As seen on my real ATX PC Desktop now, W10-64bit Pro.
    • Press Win key + P and see the settings pop up on the right and and pick "Duplicate" ,as your first test. (later try "Second screen only": works on laptops and desktops.
    If  you close the lid, on any Laptop, some can not be cured of going to sleep or turns off.  (even with the power settings for that lid are set to do nothing) If you must close the lid better test this first !
    This feature below works on laptops (mobile) only, and may not work on the very very cheap versions of your OS, like Windows HOME or Starter edition.)
    Win+X key, type mobility in the run search box, on non portable PCs this will be missing (I have w10-64bit PRO ATX Z270p), and is MISSING on all real Desktop PCs, but present on all my laptops) (see here for better examples)

    Find free programs (even for testing) that are called KILL SLEEP, find it use  it and test the PC to prove the hardware is OK.
    I free program that runs and turns off sleep is here. (  0 hits for safe)

    A RELIC : Blast from the past. (Very old Desktop Monitor) Circa years 2000 to 2007.
    (the first flat panels with funky weak short lived, CCFL lamps inside, that go dim or yellow then die or go wildly intermittent)
     What I do is dump all these in the toxic waste dump (lead is toxic):

     SLEEP MODE on this device is very odd how it works.
    Get this fact the monitor can sleep all by it's self or from sleep commands (states) from your connected PC.
    Just tune off the sleep timer (aka: power saver timer) all modern monitors are devoid of this silly features.
    Warning, if you do a OSD monitor reset, the timer gets turned bad on.

    OSD means On Screen Display, it has  tiny processor brain inside the screen now.
     The OSD has  super secret hidden deep SLEEP timer, unrelated to the PC you own, it was like version 0 EPA 'Energy STAR , malarkey.  (the reasoning was that some PCs had no sleep modes so and added it here)
    Some "Odd duck" Desktop monitor displays.  See How old LCD monitors all fail with a dead CCFL seen here. (and large list of model names too and tests and more for any screens made...)

    VF15,  see this?  1024 x 768 max.. (so windows 10 makes this PIG show "OUT OF RANGE"..

    OLD DOG LCD monitors, from say year 2002: (yah 15 years old)  (2000 to 2010 are the worst in LCD in the year 2010 LED BEGAN, best is to buy 2010 up)
    This old dog had a   INTERNAL,  timer  clock and sleep timer,  this needs to be turned off.   (No modern LCD monitor  has this  inside it now)
    Modern displays the PC side,  shuts off 1 or both cable Video Sync lines to cause SLEEP, aka , advanced VESA controls.(wiki that)
    Most of these displays are dead and or long gone now with the CCFL bulbs inside burned out. (mostly ended in year 2010)
    The Oddness here is the queer SLEEP mode , that changed later with the new VESA spec standardizing sleep modes, and on that day this timer here was DELETED forever. (2007? is my guess on year change over happened)

    Push the displays OSD menu button then MANAGEMENT item there.,  if the DISPLAY front panel OSD button is dead?, (it's locked) push menu key for more that 10 seconds, and it unlock OSD mode.
    Turn off all timers, all of them , find them all and disable them. This is CIRCA, 2000 year to 2005 (and for sure ended with LED LCD displays in 2010)
    This screen is gone today, on newer monitors. This OSD entry is for very old PCs what will not sleep years ago, so the sleep brain is inside the MONITOR only. The CURE IS TURN IT OFF.
    Note that the monitor has it's own crude RTC 24 hour clock inside the confines of the MONITOR all by itself, yah turn this junk OFF .
    This timer ended on or just after magical year 2010.
      end RELIC monitors.

    DIM list: #1  Laptops only   The errors seen can be any PC of any kind and means the DRIVERS are BAD.
    1. The control panel device  manager, shows no errors on keyboard, mouse, USB ports nor the Video Graphics device (card or chip)  ( no red marks yellow marker , no Unknown Devices)
    2. The Brightness  set wrong on the keyboard as seen below, (yours will use different keys for Dim /bright.) The key icons are a tiny sun , is a big clue.
    3. If the laptop main battery is weak the screen goes DIM by design,  remove the battery, if the screen goes bright, BINGO ! leave it out that battery run on AC only)
    4. The PCs ambient light detector feature is turned on, it will go dim in a dark room,  aka: Adaptive Brightness feature, turn it off if you don't like it.
    5. All old CCFL go DIM. (really are not all dim?, 20,000 hours usage.  10 Hours used per day for 5.5  years,  bingo you are there DIM BULB CITY or yellow /dead or intermittent CCFL tubes.
    6. The LCD back lamp  inverter card, has problems. (rare! above line is 10x more likely)
    7. The screen goes black in sleep /hibernate mode, so is not really DIM, but turn off sleep if you  do not like it turn it off in CP + POWER settings.
    8. If the screen  is cracked or full of colored lines the LCD panel is bad, or cable to it  or the chip driving this LCD is bad.
    This tells me (shouts) someone does not know how to load the OS fresh , using wrong install media and wrong drivers.
    The cure above, is get your drivers, from your PC maker. (if MS plug and play fails as sure did above)  By OS version and by PC model exactly, best is ask you OEM for the correct drivers. The above person did not.
    The #1 reason for above, is upgrading the OS, not asking the maker first, if you can. (case in point W10 does not support most old  device functional chips)
    NO 2 LAPTOPS use the same keys, ok, every maker (OEM) has there own keys to use, in all case learn to read your Operators guide.  (, are the best PC in the world)
    No 2 laptops use the same keyboard nor same the drivers, nor same keys for DIM.  This PC we push blue Fn + arrow up  or down.
    For the above keys  to work the correctly he  OEM driver must be installed , matching your PCs model exactly and OS version. (or it WILL NOT WORK) (the exceptions and advanced methods are here)
    All laptops made dim the screen on battery mode, or if  the battery is weak or battery defective. (even with batteries with shorted internal cells)
    All do this DIM until you buy a new battery and use that, or run on AC pack only even with battery removed, forever)

    Dim list #2 Desktops Only:   ATX Desktops , not Fake ones called "All_In_One Desktops" that I avoid and never cover.(them)
    Again the drivers must not look like this, showing they are bad, this is first, wrong or missing drivers will cause sleep modes to fail.

    First off Desktops have no internal screen nor any kind of laptop main power battery. 
    Never run any desktop lacking the proper driver for you VIDEO GPU chip or CARD,  get them from your OEM makers web site.

    The desktop uses only an External monitor. (best are LED LCD back lamped monitors year 2010 or newer !) "I like ViewSonic and HP Monitors (and DELL)"
    Hard failures are covered here extensively.
    Best is to turn the PC on first, then the monitor 2nd, (for testing only this is best ok?)
    This allows you to see the Monitor tell you what is bad.
    The monitor has its own tiny processor brain (ARM like)  that has a large list of errors to report for most things that can go wrong. (the OSD is the BRAIN talking to you now) On screen Display.
    The OSD will run for 10 seconds (on average) on demand even if the PC is off. (yes that too is a wise to do test)

    Testing List:  (do not skip test 1 below)  The monitor will tell you, (or in odd ways) the PC is dead. ("no signal" tops the list for that)
    1. If the  monitor fails on 2 PCs then the monitor bad,  or this timer  is turned on,  OSD timer (power saver timer) turned on, so turn it off.  (if the PCs fans (2+) are dead or silent fix that first. (dead PC)
    2. The monitor, also warns you  if the PC goes dead /sleep or hibernate, with lots of errors," cable disconnected, no Signal, no Sync, out of range, or Going to Sleep mode and goes black)  This is PC problems not monitor.
    3. A bad cable error.  If the video Sync lines fail, the monitor goes black with errors above. (some monitors just tell you going to sleep if the PC is dead)
    4. The monitor is in fact dead if the OSD screens never work with the pressing of the monitor menu button,( with-in 5 seconds of monitor turn on) if the power lamp on the monitor is dead, the monitor is dead.
    5. The Desktop PC can not really DIM any monitor, but can set it to black screen ,(black is not DIM) Black screen is sleep or hibernate modes.
    6. All monitors have there  own brightness buttons on the front panel or hidden in the OSD menu. The monitors users manual covers all this, why not read  it,  Google like this, (monitor make/model# manual)
    7. The old monitors made from year 2000 to 2010 had CCFL back lamps and all of them now are 8 year old or older and all are now dim, never seen one now, not DIM. (unless parked on shelf for 10 years)
    8. The monitor power lamp LED may have 3 modes (color LED lamp) Green power on normal, and Amber, in sleep mode.(see this link on all monitor failures vast and lots of testing)
    9. The PC software can make the monitor go black not dim, the monitor will show error "out of range" so at the PC set the video resolution to your old monitors poor resolution, even 800x600.
    10. If you suspect the above, Out Range, use windows safe mode F8, (800x600)  Most monitors made can do at least 1024x768. (read your monitors spec, learn where MAX is?  the set it to max"or stated as BEST")
    Offline testing monitor: VGA/DVI/HDMI/DP cable not connected:  (some new monitors have only HDMI  or only DP) DP = Display port technology seen on thin laptops many.
    The monitor can have 4 ports now, and the monitor scans all ports and if all are dead, it tells you that on the screen.(all do)
    The OSD window on all monitors do not run for hours on end, so it self times out,, if they allowed that the screen LCD will burn.  (
    The OSD menu times out in 5 to 60 seconds, many  monitors you can change the OSD time out delay to 60 seconds,  for more easy testing off line.
    Power on , and quickly push MENU, if OSD looks bad or is dead the monitor is NO GOOD. (turn up the brightness in the OSD first if screen is black or dim)
    The montor tests are :
    1: off line, with all video cables removed, turn on the  monitor and push MENU button 1 on the front panen of the Monitor, a second later. (no OSD now? is a dead monitor) The cure is a newer good monitor.
    2: Test 2 is chech the monitor on another PC that you know works. (easy no?) The below screen shows my PC is DEAD.

    When you see this screen test the monitor on 2nd PC that is working. (As you can see the OSD is not dim or dead so the monitor is not dead) The PC is dead (fans silent) or the PC is in Deep Sleep/hibernate mode.)
     A Dead PC. or video cable fell off or even a bad cable.

    See the autopower off, oops do not turn that on, no 2 monitors made have the same features, learn to look first and learn what you have.
    Sleep timer is present disabled,  set OSD timer to max first to test the monitor off line. As you can see clearly the screen is not dim, yellow or dead.

    Related but way longer set of tests and causes are here in my black screens of death pages.

    end saga.

    version 2.  5-9-2017,,By: Deadpool (edited lots of typo's )