How do I demote a PDC to a BDC?

A. Normally when you promote a BDC to the PDC, the existing PDC is automatically demoted to a BDC, but in the event that the PDC was taken off line and then a BDC promoted when the old PDC is restarted it will still think its the PDC and when it detects another PDC it will simply stop its own netlogon service.

To actually modify the machine to be a BDC the registry needs to be changed directly:

1. Logon to the machine as an Administrator
2. Start the registry editor (regedt32.exe)
3. Move to HKEY_LOCAL_MACHINE\Security
4. Select Permissions from the Security menu
5. Select Administrators and change the access type to Full Control, check the "Replace Permission on Existing Subkeys" and click OK. Click Yes to the confirmations dialog box
6. You can now navigate the Security menu, move down to Policy\PolSrvRo
7. Double click on the default <no name> value and change the second digit (which should be 3 for a PDC) to a 2 (which means BDC). Click OK. E.g. 03000000 to 02000000.
8. You should now reset the Security on the Security part of the registry using the same method as before but changing back to Special Access for Administrators. The permissions for Administrators should be
   - Write DAC
   - Read Control
9. Restart the machine and it will come up as a BDC

To avoid having to set security perform the registry change from the system account by submitting the registry editor via the schedule service.

C:\> net start schedule (only if not already running)
C:\> at <time> /inter regedt32.exe
C:\> net stop schedule (only if you had to start it)