I am having a similar error which SQL 2000 service pack 3a does not correct.

Error: 17883, Severity: 1, State: 0
The Scheduler 0 appears to be hung. SPID 0, ECID 0, UMS Context 0x021F7F20.

In addition, when I try to open the database, for instance to add information to a table, the enterprise manager console immediately hangs. I believe this is due to the fact that my SQL 2000 server resides on a domain controller although this problem did not occur until a month ago and had been functioning correctly after the initial install. The database IS also still functional, I simply can't access it for management purposes. When I attempted to reinstall sp3a, the installer hangs at the "validating user" step. This occurs whether I use a Windows or SQL user account (even the SA account hangs on the validating password step) to run the service pack install.