Original post by: QEII Student IT ,
At startup, hold +S simultaneously, then when the code stops, type fsck -fy, this will run a hard drive repair. Hopefully it will repair your hard drive and you can type logout to boot up as normal. If it does not work, you will need to try re-imaging your hard drive. If that doesn't work, [http://www.ifixit.com/Guide/Repair/Installing-PowerBook-G4-Aluminum-15-Inch-1-67-GHz-Hard-Drive/638/1|replace the hard drive].