Sounds like a local SAM failure. You may be able to restore the registry
from backup or perform the following task from a "parallel" install of the
operating system on the same computer.
Copy all of the backup information from the \winnt\repair folder to the
\winnt\system32\config .
Your best bet though would be to restore the registry from backup.
Buz Brodin
MCSE NT4 / Win2K
Microsoft Enterprise Domain Support