How to remove dead domain controllers from AD
Log on to your domain controller and go to Control Panel –> Administrative Tools –> open ADSI Edit. Click on ADSI edit and choose connect to….
On the Connection Settings window on the name line/section write Configuration. On the Connection Point section under Select a well known Naming Context choose Configuration. On the last section called Computer, select your preferred Domain Controller. In another note if you don’t want to use your current credentials click on advanced and from there you can specify credentials. Also it is possible choose port number and you can choose protocol. Now click ok (to close the advanced bit) and again ok. Now browse down to CN=Sites and then click on your site, and open it, browse down to CN=Servers and delete the servers you want to remove.