Upgrade Problems

Dear there,
W’ve done an upgrade for our PDC from NT4.0 to Win2000. Before the upgrade we diconnected the PDC off the network (because we thought this will be safer) , But now we experiencing some problems related to the Backup domain controllers in there relations with the current upgraded DC, where one of the BDCs is trying to be the PDC while there is already a PDC (The upgraded one)!!