When you promote the server to domain controller and failed, you are still left with its metadata inside Active Directory Domain. Because of this, you may face some of the following issues: 

  1. When you again promote the same server with same NetBIOS name, you will fail because of the same objects reside in active directory
  2. You won’t be able to promote a new server to domain controller because of replication issues and failure of FSMO role owners.

It is advised to clean the AD metadata whenever you fail in promoting DCs. This article can help you with this. 

Open PowerShell with elevated privileges and execute the following commands in sequence.

Step 1. Type ntdsutil and hit enter from keyboard

Step 2. Type metadata cleanup and hit enter from keyboard

Step 3. Type connections and hit enter from keyboard

Step 4. Type connect to server <NetBIOS or DNS name of any domain controller of the domain you would like to delete failed DC from>

Step 5. Type q and hit enter from keyboard

Step 6. Type select operation target and hit enter from keyboard

Step 7. Type list domains and hit enter from keyboard

Step 8. Type select domain <Domain number in which failed DC is located> and hit enter from keyboard

Step 9. Type list sites and hit enter from keyboard

Step 10. Type select site <Site number in which failed DC lies > and hit enter from keyboard

Step 11. Type list servers in site and hit enter from keyboard

Step 12. Type select server <Server number of failed DC you want to remove> and hit enter from keyboard

Step 13. Type q and hit enter from keyboard

Step 14. Type remove selected server and hit enter 

Step 15. Ignore the warning and click YES

At point this point the DC should have been removed. Repeat from step 6 if you would like to remove more failed DCs.