Are you able to get in to safe mode? This would allow you to diagnose what got corrupted and get your data off before anything more drastic. Could be a virus as well, so use a virus boot disk to check.
If you have critical files on your "C" drive and absolutely need to retrieve before a re-install perhaps
you can use this LINUX solution
New to 2000. Machine displays a BSOD stop error on boot, "registry file failure" ...system32\config\software or it's log or alternate is corrupt, absent or not writable. I seem not to be able to do a repair install of 2000, as it warns of wiping out everything, and the LAST KNOWN GOOD STATE fails. How do I fix?