I have had a variety of problems with my G4 PowerBook. At first they happened only when it woke up from sleep. Rapid horizontal streaks would appear and sometimes go away. Othertimes the display would freeze, and I would need to boot up again. At times I would get a black screen on first starting up. I had the unit repaired, and was told they replaced the display. Things were good for a week, and then the same problem came back, along with a new one: a (occasionally flashing) blue screen after boot-up, just at point where the desktop should appear. I thought the "blue sceen of death" was a Windows-only problem!
Any ideas? Thanks.

It sounds like the logic board is the culprit. Hook your laptop into an external monitor, and see if the problem replicates itself there. If it does then you're logic board needs to be replaced.

-Bradley
POWERBOOKMEDIC.COM

ok, i hooked up to an external monitor, and when the screen on my powerbook G4 500MHz was ok, and i could access the system preferences long enough to load the display settings for "arrangement", it worked fine without the main display flickering and acting real strange. it works sometimes, but most of the time it looks like a tv that doesn't have the vertical/horizontal settings adjusted properly (remember how that looks?) when it stops flickering i can use it, but when it's flickering all i can do is shut it down. HELP!???

If it is flickering on the external monitor, then your Video is bad on the logic board, and you'll need to have your board replaced.

-Bradley
POWERBOOKMEDIC.COM