Demoting a PDC to BDC Status
If you need to demote a PDC manually and the preceding procedure won't work (possibly due to hardware or Registry-related failure), try the following approach to perform a PDC demotion:
Notify the users that the PDC will be shut down.
On the PDC, open the Control Panel and then the Services applet.
Stop the Server service. This prevents new user logons while the change is underway.
Open Server Manager.
Select Properties from the Users menu and click the Computer button.
Click the Disconnect All button to disconnect all users.
Select the PDC.
Select Demote To Backup Domain Controller from the Computer menu.
Restart the Server service on the former PDC.