PC won't turn On
No matter what you do, you can't get your PC to turn on.
Battery not seated correctly
Make sure the battery is seated in the battery slot and you hear a click. You may find Dell Latitude D820 Battery Replacement helpful. You can verify by running your hand over the battery and should be rather smooth.
Note: Some of these batteries have a button you can push to see if there is any charge as well.
Battery is drained / Bad battery
First make sure the AC adapter is securely plugged into the laptop and the power adapter has a green light (if not check the outlet, it maybe on a switch). You should be able to power on the laptop at this point.
If your laptop turns on but only while connected to the outlet and adapter you can purchase a replacement battery. Dell sells batteries and you will find many different sites that have them as well
Shutdowns down unexpectedly
Your laptop maybe overheating if you are able to work for a short amount of time then it shuts down unexpectedly. (This is not the sole cause but a good indicator)
So questions that may help determine the cause:
Is there any error messages before or after the shutdown?
Open Event Viewer to see any additional messages or logs of the system recording the event.
Memory going bad
If you are receiving BSODS (Blue screens of death) and short amount of time to work on your laptop then you may have a bad memory module(s). You can remove one at a time and try using the laptop for an extended period with one removed and see if it happens again. If it does not, replace the module you have removed. If you still receive errors then it maybe a combination of these things or something else completely.
Central Processing Unit fan may not be turning on
If you suspect the fan is not turning on, it could be clogged with dust, burnt out or may have come unplugged from the motherboard (logic board)*.
*Note: You will need to open your laptop to check this.
Graphics Card fan maybe malfunctioning
Nothing on the Screen/Bad display
It is possible that it appears nothing is happening because the display is bad. Check to see if anything shows up when you press the power button. If you see the BIOS/POST screen, then nothing, it is possible a misconfiguration occurred which can be corrected in Safe Mode.
It is also possible that the backlight bulbs and/or inverter have failed. Examine the display under a very bright light while the computer is running. You may be able to discern elements of the desktop or login screen. Backlight bulbs are very fragile, and you are far more likely to break a replacement bulb than get it to work correctly.
If the Latitude D820 is similar to the Latitude D620 there is a small board in the bezel space below the display panel. This is the inverter. If you replace a naked panel and still have the same symptons, (Faint display only discernible under bright direct light) it may be the inverter board that is bad.
Check video card with external monitor
To check to see if the video card is working you can plug an external monitor into the laptop (VGA port on the side) and see if an image is displayed (it maybe necessary to use the FN (function key)) to toggle the display. If you connect an external monitor before powering up the laptop, you should see the Dell BIOS and Windows splash screens on both displays.
Time to replace the display ?
If you have tried both methods and are unable to produce a video, output then it is possible the display is bad and must be replaced.
If you are still having problems with your device or have not come upon a solution that works for you, it may be time to call in a professional.
Bad logic board
If you have continuous issues or none of the previous symptoms were resolved, then the problem most likely lies in the logic board.