Inspiron 640M LCD backlight won't turn on

This problem usually happens overnight when I have my laptop lid closed. When I wake up the next morning, the LCD backlight won't turn on after the BIOS screen. I've tried pressing the power button for 60 secs (after removing the battery) to discharge static electricity, but it doesn't work. The laptop usually works again after I've closed the LCD screen several times and leave the computer off for about 1-2 hours. Does anyone know the real cause of the backlight not turning on? LCD works fine btw b/c I can see stuff on the screen, just w/o the light. Is this caused by a malfunctioning laptop lid close switch? If so, then wouldn't the computer also be put to sleep when it happens (but how come my laptop doesn't actually go to sleep)?

EDIT: I am able to replicate the problem sometimes when I change the angle of the screen while powered on or when I turn on the Wi-Fi.

 

Update: OMG it happened again while I was typing something, the screen went completely dark. It seems rebooting got the screen working again. But I wish it were this simple. Sometimes, rebooting won't even get the LCD backlight to turn on...

 

Okay guys, I've figured out the problem was with the LCD screen. I've already replaced it and now works again.

Also, I don't want to throw out the problematic screen since it was working fine. Has anyone had a similar problem where they replaced the backlight inverter and got their screen working again?