Hi, My iBook G4 was frozen. I could not use the restart or shut down option. I had to use the power button. I powered it off. Waited a few minutes, then pressed the power on again. I can hear the start up tone, but only a folder icon appears with a blinking question mark. Then the question mark disappears and a simple blank folder icon remains. Can you please tell me what is wrong, and how I can fix it? Thank you!