Cannot start W2K

I have two 20Gb hard disks, one with win2k and a second with winme. I usually use win2k but after running fine for over a month win2k will not start. All I get is the dreaded Blue screen and error message: TOP:c0000218 {Registry Failure} The registry cannot load the hive (file): or its log or alternative. Systemroot\system32\config\SOFTWARE. it is corrupt, absent or not writable
I’ve tried repair from CD rom and back up disk, but no joy, its still the same.
Any help!