I turned my PB off this morning to give it a rest; when I tried to start it back up again this afternoon, it won't boot OSX. I get the silver apple screen, then the blue startup screen, but it just hangs there. I have tried holding option-command-shift-del, but no success. I have also tried holding down the X key. I'm running 10.4.1 on a PB G4, help please!