BIOS and WINDOWS have complex , sleep, hibernate or adaptive dim and power dim modes.  See fast dim reasons here.

All laptops made dim the screen on battery mode, or if  the battery is weak or battery defective.
All do this until you buy a new battery and use it, or run on AC only battery removed)
See all related monitor problems here. (internal or external)

Windows 7 to 10 , Microsoft keeps changing how to use Presentation modes, (no sleeps of any kind) to run  TV as  screen or any real Projector made.
A blast from the PAST? (year 2000 to 2010)

Or those old relic CRT's; really?"Cathod Ray Tubes?"

Ignoring my better judgment, I will do one page on this bit flipping topic, as it relates to SCREEN DEAD complaints.(which I cover to  the extreme)

I will not try to explain fully why sleep modes exist.  (wiki it?)
The hardware is complex in this regard, due only to the demands of USA Energy Star,  mandates,  to reduce power , when the PC is not doing useful work. "Save the planet Green stuff"
All modern PC's here go to screen blank status, after timer expires and no keyboard or mouse activity is discovered. (called sleep or hybernate mode, the latter is just deeper less power mode)
The PC can fail 2 ways, go to this mode when you don't want it to or never goes to this mode, or takes too long or too short of time to reach this state (sleep or hibenate) { it is programmable by you}
If using your PC as part of projection system for a movie theater(home?) or for a business, power point presentation, how fun is it , if the screen goes blank.?
The laptop has 2 auto dimmers modes too, for its internal screen.
The Laptop chips run the local screeen directly and can dim  the LED back lights  from even the BIOS LEVEL (even with the HDD missing)
The OS (operating system ) can set the the local DIM mode, on any Laptop or put it to sleep.
The OS can also do adaptive Brightness mode, based on ambient light in the room for go to full brightness out doors.
The laptop has DIM mode when running on battery power only. (No desktop has this)
Same with the age old Screen saver! if you set it to blank screen option, (yes even W10 has it, even though CRT displays are now history as is phospher burning, but some like it for fun)
Screen Saver is now hidden in W10,  click settings icon, click screen lock, the on the bottom screen saver but turn it off. (it is by default) If it was set to Blank, then bingo?  All modes this page have timer.

It will dim if you turn on "Adaptive  brightness", photo1 below.. 
This  feature uses the magic trick of using the web camera to dim the display in a dark room, or the opposite.  (or ray of light, leaking past sides or holes of  Venetian blinds? fooling the camera? )
If one uses black tape over  the camera (like mine) this feature will cause the camera to go blind, and the OS to see darkness endlessly, and go to dim brightness, set the  ADAPTIVE bit as you like,  seen in photo 1. (mine is off)
I looked in my Laptop PCs BIOS and and the configuration screen there has  check mark for 'Built in ambient light sensor"  so if you don't like this, turn it off in BIOS, this will inform the OS not to use it. (depends on OS type and versions)
My Laptop does NOT have a power loss, dim mode defeat, its not listed in BIOS at all. (so can not be defeated at this level)
If the BIOS dim works and the OS does not work as  you  want, then change it as per below screens show.
My desktop has no auto-dim modes, only the manual dim in the OSD screens of the screen brain itself.
All external screens have normal sleep modes. (more than one) (2002 or newer) the relic monitors , some HP have an internal power saver ( and early form of SPEEP).

The Power ICON in the Control panel , lets you see the many modes to flip on or off or the delay.   Turn them all off.

To prove WHAT'S up with that ?, is easy by doing any/all of the following. (after turning off all those features told above)
On my 2010 Laptop the screen  aways dims when the AC power pack is disconnected , in BIOS pages even the BIOS F1 page, information DIMS or even running Freedos OS on my memory stick it DIMs.
As you can see my PC has BIOS powersaver DIM mode too, built in, that even dims with the HDD and DVD drives both removed.

  1. On old display monitors over 10 years old , they can  have a CCFL back ground lamps (not LED)   (monitor screens have vast failure modes) Yes they can do dim or even turn YELLOW.
  2. If you run below old relic HP monitor from 2002,  push the OSD button and turn off this silly reclic (now gone) POWER SAVER mode, that is only inside the actual monitor menu's. See last photo (page) below.
  3. Try another display ? Good now? Even a laptop has a VGA or HDMI jack on the rear, to connect up another screen to help solve this riddle.. (if this test passes , your other screen is failing)
  4. External screens (good) will not power dim , like in a laptop, but do go to sleep or hibernate (black screens) on commend from the PC VGA jack.

The below is checked first by the tech. or users,  if set wrong, set it as you like.
Click control panel  then click the power Icon and check each line 1 by 1 below,  and turn all that GREEN stuff off, for now , to prove this is or not the cause of your screen issues. Set it as you like.
If only windows fails, then Windows is set wrong below or currupted or infected. (if all tests fail?, it's bad hardware or BIOS set wrong, "configuration page")

Photo 1: (in the control panel big as day)  There are vast number of bits to flip here, for sure on newer and more complex PCs of any kind, what I do is turn on, Presentation mode.

Why MS insists on tiny CP screens for 25 long years,  dang... 
Here are some more there,  Photo 2:

Read each line carefully above,
ponder each one and turn them all off.  (btw: these same screens turn off other things, you may NOT LIKE,  like wifi or USB ports)!
(on my desk top all this GREEN stuff are OFF or is not available at all on any PCI VGA card, but sleep/hibernate sure is there, just no dim modes there.)
I run my desktop in presentation mode. (that old name is gone at MS,  but we can still do it, turn off Sleep and Hibernate)
If you want DIM to work, and does not , check BIOS configuration pages first....!
In most cases folks want DIM off or Sleep off or only the timer set longer. Do it now. "See it works"
 if not?, then the OS is corrupted or virus infected or the HP drivers for the screen GPU are wrong or missing. (F11 key pressed at power one , reloads the OS back to Day1, this does work, if your PC is not slammed.


Here is W10 , that is now stuck in  power saver mode...  on Modern Laptop. (Elitebook , HP)
 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 photoshop(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.
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/intermittant.  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, (projectors or  using any KVM switch(reason#1) that love to fail (PC out of the box sure) (this assumes the laptop lid is never closed below)
If any chip in the PC (vast numbers of chips) go 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 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. (hibernete 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 to set like 20 bits there to get it like you want,  a real pain that is. CP = Control panel.
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 go to start search , paste in "presentationsettings.exe" (with no quotes) (fails on desktops)
  • 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 asleep or off.  (even with the power settings for that lid are set to do nothing)For sure test this last or avoid it.

A Blast from the past. (the first flat panels with funky CCFL lamps inside, that go dim or yellow then die)
(no great fun this old beast, it's a relic of the past)  SLEEP MODE on this device is very odd how it works.
Learn that older screens than below, there is no OSD brain back then and the power switch LED lamp colors change telling you if the VIDEO signals are lost (I will not cover any this old , google it)
OSD means On Screen Display, it has  tiny processor brain inside the screen now.   The OSD has  super secret hidden deep SPEEP timer, unrelated to the PC you own, it was like version 0 'Energy STAR , malarkey.
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....

OLD DOG LCD monitors, from say year 2002: (yah 15 years old)  (2000 to 2010 are the worst in LCD
This old dog had a SUPER SECRET INTERNAL,  time date 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 caumonitors_and_screens/CCFL-H3LL.htmlse 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. (mosly 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.

Push the display's OSD menu button then MANAGMENT 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 was removed in monitors in year 2010, (approx) this timer malarkey.
  end RELIC monitors.

DIM list: #1 
  • The Brightness knob or OSD settings or the laptop brightness is turned down, so turn it up.
  • The Laptop battery is bad or dead or weak  or shorted cells, and the Laptops brain is confused by that , so run with no battery (or replace it)
  • The PCs ambient light detector thinks the room is dark and is not,  (disable this to test this theory)
  • The CCFL are dim. (really are are now, 20,000 hours usage.  5 yours a day for 10  years,  bingo you are there.
  • The CRT is dim.
  • The inverter has problems.
  • Sleep mode is not a dim mode nor is Hibernat. DIM is just  DIM back lamps. There is cause.
  • The monitor is bad, if it fails on 2 PCs , bingo  bad.
  • The software is not usually the cause, but if the windows controls fail to work (laptops/notebooks), bingo for bad drivers.

end saga.

version 1.  5-9-2017,,By: Deadpool