Do you have any tape backups of the OS?
Or an alternate network boot image that you can get to through the network. You may have to boot the CD and then start an install and select an option for network restore or from a network tape or Silo backup???
Breen is correct that maybe your mirror disk might be good or if you have an ALT Boot path. All my servers have a PRI and ALT boot path.
Kelam *crosses his fingers*
My brain is your brain...