Good possibility the Tristar IC chip is going bad, or the solder balls under it are cracked. If you know how to micro solder put in a new chip in. microsolderingsupply.com If thats not it you could have a short to ground on VCC main. We change them at our shop all the time.
Have you tested your battery and your power cord? They are notorious on Dells for crapping out. Sounds like it not getting enough amps to charge the battery or the battery cells are about done. I would start there and then move to software related diagnostics.
Could be the cable on the hinge side that is getting worn. Try moving the lid to and fro and see if that alters the display - either better or worse. If so start there with replacing the LCD cable or check the connection.
