Here are two things to know about your Windows Server 2012 Administrator password (Works exactly the same in R2)
The whole process is remarkably easy and quite quick.
To reset the password on your Windows 2012 server, simply complete the following steps:
Boot from the Microsoft Windows Server 2012 DVD
From the Windows Setup menu, click “Next”.
Then select “Repair your computer” option
Now, click on “Troubleshoot”.
Select “Command Prompt”.
At the command prompt, run the following commands:
c:
cd windows\system32
ren Utilman.exe Utilman.exe.old
copy cmd.exe Utilman.exe
Close the command prompt and then click “Continue”. The server should now boot and present the logon screen.
Here press Windows Key + U. You should be presented with the command prompt. You can now change the password.
Type the following command:
net user administrator NewPassword123
Close the command prompt and you should now be able to log back onto the server using the password you have provided in the last step. Once you have verified you can log on to the server you will have to restore the original Utilman file.
Open “Command Prompt”. and run the following commands:
c:
cd windows\system32
ren utilman.exe utilman.exe.new
copy utilman.exe.old utilman.exe
Close the command prompt.
You should be back up and running as if nothing ever happened.