How do I reinstate my old PDC back into the Domain as the PDC?

A. It is not possible to have 2 PDC's in a domain so assuming the machine crashed, i.e. has not been demoted to a BDC before being shutdown, then when it starts it will still be configured to be a PDC

1. Start up the old PDC machine
2. Logon to the machine as an Administrator
3. Start Server Manager (Start - Programs - Administrative Tools - Server Manager)
4. The machine will still be described as a Primary Domain Controller, however its icon is just a wire frame and it is not acting as a PDC, i.e. it does not authenticate logons
5. Select the machine, and from the Computer menu select "Demote to Backup Domain Controller"
6. Click "Yes" to make the change
7. Once the machine is a BDC, click on the computer again and from the Computer menu select "Promote to PDC"
8. Click "Yes to make the change
9. Server manager will then automatically demote the temporary PDC back to its BDC status and promote this machine back to the PDC