I'd suggest Microsoft support, but SQL 2000 has been out of support for 3 years or so.
Maybe reinstall SQL and reattach the user databases, but I don't know if that will help. Probably a good idea at this point if you get a competent SQL consultant in to help.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability