Server, not participating in domain

I have a server that “was” part of a domain as a backup domain controller (NT4 Sp6). But when I did some changin of machines etc. now I keep getting a message in the event log that says that machine and another machine (the actual PDC) BOTH think they are the PDC, and thus it does not play well in the domain, i.e. does nto show up as a proper BDC. How can I fix this short of doing a full re-install of NT.
Thank you.