Monitor my laptop appears to be off, even though it is on. the power light works but the screen remains blank like it is still off

The problem is cause due to one of the following: the backlight or the display, check your monitor brightness settings. Sometimes your brightness may accidentally have been all the way turned down, resulting in a blank/dark screen. The monitor controls are on the keyboard, directly above the numeric keys.
Look closely at your laptop's screen if the steps do not restore power to it and if it remains blank. Can you see a faint image on the screen? If so, the backlight may be off due to the LCD "lid close" detector malfunctioning. This malfunction likely happened due to the lid close switch being stuck in the "closed" position even though the lid is open. The switch is located beside the LCD's screen hinges, and tapping the switch a few times should unstick it.
Use an S-Video cable and plug your laptop up to an external monitor, such as your television set. With the laptop and TV hooked up, turn both on and see if your computer's desktop is displayed on the TV. You can also use a fifteen ( 15 )pin monitor desktop monitor by connecting it to the blue fifteen ( 15 ) connector at the side of the laptop if you cannot see anything on screen it is the display problem. If it is, your laptop's display needs to be replaced. If not, your motherboard and/or video subsystem may need to be completely removed and replaced.

You would be well advised to hit F8 and do a safe mode. Then check the disk. More details here: http://annoyances-resolved.blogspot.com/2009/09/laptop-wont-boot-and-shows-blank-screen.html

try connecting a seperate screen - if it works then you back-light mught need replacing. if you see nothing still then you might want to take the laptop back to where you had it fixed

Try taking out the hard disk, plug in power and see if you have a display on your screen or external monitor. if same thing happen, try taking out the memory card. If you hear a beep sound it's a faulty mem. card, if no beep sound appears I suspected it's a motherboard faulty.

First, confirm that it is the screen itself. Connect the video output to a known working monitor and then power on your Thinkpad. if the known working monitor behaves the same way you can rule out the laptop's monitor as the source of the problem. This may be the BGA, Ball Grid Assembly, leadless soldering problem related to video chips on the motherboard, but first test the monitors.

First if you have a extra monitor try to plug it in and see if it works. If not then check your video card. or get into the computer and try and remove and reseat the memory. Sometimes by just doing that can solve the problems

This looks like a problem with the video card or the power supply to the monitor. Try connecting a different monitor and if you still face the same problem then probably you may need to have a look at your video card or its connection in motherboard

Did you switch displays to the external video? Try hitting the Fn key and whichever function key at the top of the keyboard has a little TV screen icon over it at the same time.

Self-Test Feature Check (STFC) Your monitor provides a self-test feature that allows you to check whether your monitor is functioning properly. If your monitor and computer are properly connected but the monitor screen remains dark, run the monitor self-test by performing the following steps:

1. Turn off both your computer and the monitor.
2. Unplug the video cable from the back of the computer. To ensure proper Self-Test operation, remove Analog (blue connector) cables from the back of computer.
3. Turn on the monitor. The floating 'Dell - self-test Feature Check' dialog box should appear on-screen (against a black background) if the monitor cannot sense a video signal and is working correctly. While in self-test mode, the power LED remains green and the self-test pattern will scroll through the screen continually.
   
4. Turn off your monitor and reconnect the video cable; then turn on both your computer and the monitor.

If your monitor screen remains blank after you use the previous procedure, check your video controller and computer system; your monitor is functioning properly.

Thanks
proton