Forgot Password Server 2012

This works on Windows Server 2008 R2 and Server 2012 R2. You will need Windows Server 2012 Installation DVD to reset password.

Reset Windows Server Password with Installation CD

1. Insert the installation disk to your locked computer, restart. When following interface appears. Click “Repair your computer”.
2. A dialog with several options pops up, choose Troubleshooting tools, then Command Prompt.

3. At the Command Prompt, type the following 2 commands. (if your correct C: drive doesn't appear, find it first and use that drive)

   copy c:\windows\system32\sethc.exe c:\windows\system32\sethcbak.exe
   
   copy c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe
   

4. Restart your computer. On the login screen, tap Shift key five times and you'll see a command prompt screen in administrator mode. OK, type net user UserName NewPassword (replace the UserName and UserPassword with the one you need) and press Enter key. The user password will be replaced with new one. Close the window and then you can log in that user with new password.

5. Once you've logged in successfully, copy the real sethc.exe back in place to prevent a random person from repeating your feat (without at least rebooting the machine):

   copy c:\windows\system32\sethcbak.exe c:\windows\system32\sethc.exe
   

I regularly use Offline NT Password & Registry Editor:

http://pogostick.net/~pnh/ntpasswd/

However, I cannot vouch on whether it works well for Server 2012 or not. As usual, take precautions and perform a backup before attempting this.