[cartomat]

As the subject implies - the bottom 1/3 of the screen on my 500mhz G4 tibook goes black or freezes. I can tilt the screen slightly forward/backward to fix it temporarily but it seems to default into the frozed state.

I have found that if I hold the screen at a certain angle I can maintain a steady refresh rate for the lower portion of screen.

Might there be a loose cable or is my screen toast? Also, every once in awhile the whole computer freezes-up.

[euphras]

Yes it sounds like a loose/broken cable coonection. Are you still under warranty (AppleCare)?

[Detrius]

The fact that the whole computer freezes up says this is probably a logic board problem. If you have an Apple Hardware Test CD for this machine, run it. It will likely tell you that your graphics chip is bad.