My screen does that every once and awhile. I can still see a shadow of whatever should be on the screen, but I can't make out anything. I use this to fix it:
http://i.walmart.com/i/p/00/04/42/77...18_215X215.jpg
Kidding. I just reposition the screen and it works fine. I find that if I press down the screen towards the keyboard, it'll light up. The further back I position it, the more frequent it happens.