How can I fix dark screen on my Acer?

Ok, so...
I got Acer Aspire 5100 (Windows XP). My screen went dark.
The screen's not dead; when i push "fn" + "f5" the screen becomes alive for few seconds, then goes dark again.
I tried reinstalling the drivers, whole OS, I tried "fn" + "right arrow" tip...dunno what might be wrong? anyone got anything on this? :)