There is a known video problem with some iBooks and yours may be one of those unfortunates. Apple hasan extended warranty on the faulty machines.
Post the serial number of the machine here and I'll check for you
This one has me puzzled. In a nutshell, my iBook G4 boots up normally, with the normal desktop appearing. Then after a couple minutes the screen goes blank. After about 15 seconds it starts sequencing through a full screen of white, then red, blue and green. It then starts the sequencing all over again. The only way to stop this is to pull the battery. When the battery is re-inserted the cooling fan goes on. When the fan shuts off the computer can then again be re-booted and the entire sequence starts all over.
What can be causing this? Is it the hard drive or somthing else?