Computer screen is dark

The screen may become dark if Picture mode is set to Cinema or Custom. If the screen continues to remain dark after changing the picture quality mode, go to the Backlight, Picture, Brightness menu and adjust the brightness to your liking. When Power Saving is fixed to Low or High, the screen becomes dark. Some TVs have a Light Sensor so the picture will just become brighter or darker depending on the lighting in the room.
You can also try programming from a different source, like a DVD player or VCR to check whether the problem is caused by the device that sends the signal to the TV.

When you
When you power up your computer and the monitor screen remains dark, the problem can be either be associated with your monitor, or your computer power supply/video card/motherboard or CPU. Perform the following tests to isolate the problem to either the monitor or the computer.
1. Turn off you PC and monitor. Then verify that the 15 pin video data cable connectors are fully inserted into their receptacles on the rear of your PC and on the rear of the monitor and they are tightened down. (on some monitors the data cable is hard-wired to the monitor). Then make sure that both your monitor power cable is securely plugged into a working AC power receptacle. (You can temporarily plug a lamp into your AC power receptacle to make sure you have a good source of AC power).
3. Turn on the power switch on your monitor. The amber colored LED on your monitor should come on. Then turn on your PC. The fans in your PC start to run and continue to run and the LED on your monitor should change from amber to green.
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Now if the monitor led remains amber and the screen stays dark you either have a bad monitor or a problem with your video card, motherboard or processor.. Try using a different monitor. If that doesn't solve the problem, you need to have a PC technician test your computer.
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Best regards,
Yavacotech

If there is a dark line with two sources such as a dvd player, and a game system, or a cable box, then the tv will need to be repaired. If not from two sources then the issue is with the only source causing the black line.

press F5 in the keyboard the light should be back or check the keyboard in the computer in the top botton where you see a sun design press that one you shoul have two of those 1 for put the light dark and the other one for put the light back good luck

Find yourself a dark room or wait for the night to come. The darkest monitor adjustment could somehow reveal some light when there are no other light source available.

You may also hook a conventional CRT monitor and make your changes (such as bringing your computer back to its original settings). The darkest adjustment in CRT monitor could still render discernible displays.

A quick Google search turned up a couple of sources for generic replacements:

http://www.lcdparts.net/CCFL1.aspx

and

http://www.ccflsurplus.com/laandmoba.html

Looks like they might be promising. A possible source for the original HP part might be Vance-Baldwin (www.vancebaldwin.com). I have purchased other HP parts from them.

If you can still faintly see data on your screen, it will be a faulty backlight in the panel most likely.

LCD panels have fluorescent tubes in them that provide the light needed to see the data. If one of these goes faulty, the circuit that drives it will turn off ALL the backlights, giving you a black screen.
Note: a faulty circuit that drives the backlights will often give the same apparent fault.
You will need to take the monitor in for repair.

Put a light up to the screen to see if its just the light. If you can see your background its the light or a light setting, otherwise it will need to be repaired.

From what I understand there may be a problem with the power circuitry used to light up a small fluorescent light that is the actual light source for the display. The TFT display itself doesn't produce it's own light, and if you point an external light source to the display and see program windows & other things the display itself is fine. Your problem can be solved with relative ease, but only in a computer service because it demands some components to be changed.