You'll find that the Knowledge Base article about Disk Utility and fsck mentions
If fsck found issues and has altered, repaired, or fixed anything, it will display this message:
*** FILE SYSTEM WAS MODIFIED ***
That you're getting the message repeatedly indicates your hard drive and/or OS X System is severely corrupted.
Did you also boot from the OS X Install disc and run Installermenu> Disk Utility> Repair Disk? What did it report? Did Repair Disk report making any repairs? If it does, run Repair Disk again until it either gives an all-clear or an unrepairable error message. Let us kow what Disk Utility> Repair Disk reports first before proceeding past the Disk Warriior tip below.
If Repair Disk reported 'keys out or order', 'overlapped extents', and/or 'b-tree corruption' that it was unable to repair, your best bet would be to buy a bootable copy of
DiskWarrior.
If Disk Warrior is unable to repair the drive and you have access to another Mac with a Firewire port and OS X, you can try booting the damaged Mac in
Firewire Target Disk Mode so that you can
backup your data. A copy of SuperDuper! or Carbon Copy Cloner (see
Apple link to third-party utilities) would help with the backup.
You could try an
Archive and Install but if there's underlying disk directory corruption as reported by Repair Disk, this won't directly help and can leave the Mac unstable. It may, however, let you boot up long enough to backup your Home folder onto CD-R or external Firewire hard drive. A long-term fix if Disk Warrior can'r repair the drive is to do an erase and install, including the option to zero the hard drive, followed by restoring your backed-up data. (Zeroing the drive will map out any bad disk sectors.) But let us know what Disk Utility> Repair Disk reports first.
