My ibook g4 1.33GHz has issues with start/restart. Reinstalled Tiger. Yet it continues to "crash' to black box-- which says I need to restart computer. If I shutdown and leave the computer alone for sometime, it will reboot into OS X and it's usually good until you ask for restart. The screen stays black with no reboot. I shut G4 down and restart into Open Firmware with message--invalid memory access. At this point, if I type in mac-boot, a folder with question mark shows up.. If I type shutdown, it shuts off fine. Upon reboot the screen is black or if I attempt to reset pram, it goes to Open Firmware with IMA message. If I try to reboot with Install CD, it goes to Open Firmware. It I set the G4 aside for an hour or so, it usually reboots fine but, if I tell it to restart, it either goes black or ends up with Open Firmware. When the G4 is running in OS X it functions fine.