In the case you have a failed domain controller where there is no option to delete him using dcpromo utility, yau have to follow the above prcedure:
Login to an active domain cotroller and open a command prompt.
C:\ C:\ntdsutil C:\metadata cleanup C:\connections C:\connect to server servername C:\q C:\select operation target C:\list domains C:\select domain 0 C:\list sites C:\select site 0 C:\list servers in site C:\select server 0 C:\q C:\remove selected server
After removing the server with ntdsutil we have to remove him from the Active Directory Sites and Services snap-in and from the Active Directory Users and Computers.