BDC is not doing it job

Our PDC is havning problem and we took it down. After taken of the PDC, the BDC doesn’t kick it. We tried to promote the BDC to PDC, but it just doesn’t log in to any database, server manger, user mananger. What is it that causing problem? We check the even log and see that BDC and PDC is synched fine. What do I need to do to make sure that BDC is doing it job when PDC is down.