W2K Domain Controller Gone Whacky

I have a W2K domain controller that seems to have lost it identity to the domain controller group. It still appears in the group (but only for the domain controller that was upgraded from NT 4.0 to W2K). The server in question was added afterwards as an addition domain controller. It was turned off for a while and another server was added as a domain controller. When I turned it back on, unsers are unable to logon to the network. I can't demote it because it won't recognize the main server. I plan on rebuilding the server so I really want is how do I remove it from the domain controller group since I can't demote it.