I am new to MAC computers and not sure how to fix problem. I have a MAC OS X 10.5.8 PowerBook G4. Computer freezes up and force quit does not work, so I have to restart comp. at start up a box with a picture of the world blinks off and on, then a small file or folder icon appears with a face then a question mark blinking back and forth, then screen turns blue after awhile my desktop shows up. I have a Mac OS X book but cannot find sufficient information to figure out what to do. Any help anyone can give would be greatly appreciated.