yep, backlight problem, probably a short in the wiring. my sister dropped her iBook 700, and has exactly the problems you mentioned. she can't tilt the display more than 90 degrees, or else the backlight goes out; you can still see the screen if you look hard, there's just no backlight. sometimes, i could get the display to light if i closed the iBook, then opened it again slowly.
an apple store genius confirmed the backlight issue, said that a repair would be about $300 or so, with about a week turnaround time.. (unfortunately, my sister was 2 months out of warranty).
if you're still under warranty, you're in luck. if you can still get applecare, i'd get it, because it's actually cheaper than what the repair would be.
tr