Windows modes that confuse folks, sleep, hibernate or adaptive dim and power dim, etc.
W10 will be my only examples.    For monitor problems see this.

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 displays over 10 years old , they can  have a CCFL back ground lamps (not LED)  and love to go dim or act odd (flicker dim, turn yellow, act in very odd ways)  << means its bad or its inverter supply to it is bad.
  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)

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)

Batteries love to fail, then you ignore that? and wonder why the screen dims?, it dims because the PC thinks (and knows) the battery is bad or weak or discharging and goes to DIM mode.
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 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. (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.

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 here. (and large list of model names tool...)

VF15,  see this?  1024 x 768 max....

OLD DOG LCD monitors, from say year 2002: (yah 15 years old)
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 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.
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.
This old screen has a TIME OF DAY CLOCK chip inside. (yes, very very odd, this idea... legacy bs.)
Your manual covered all this, per this page.
  end RELIC monitors.

Where we will never go is the relic  CRT ERA ever.   ( some have no OSD at all , no sleep at all then, made in the last CENTURY, LOL)
Forget them. Please.. end it. (recycle  center this Pig) Most CRT this old are a fire or shock hazard now)
The huge heavy glass vacuum Cathode Ray Tube.  

Vaccum tube technology ends now.

end saga.

version 1.  5-9-2017,,By: Deadpool