Start --Run-- dcpromo /forceremoval
Windows Server 2003 domain controllers
By default, Windows Server 2003 domain controllers support forced demotion. Click Start, click Run, and then type the following command:
At the Welcome to the Active Directory Installation Wizard page, click Next.
At the Force the Removal of Active Directory page, click Next.
In Administrator Password, type the password and confirmed password that you want to assign to the Administrator account of the local SAM database, and then click Next.
In Summary, click Next.
Perform a metadata cleanup for the demoted domain controller on a surviving domain controller in the forest.