Boot from Microsoft Windows Server 2012R2 DVD/ISO. From the Windows Setup menu, click "Next". Select "Repair your computer". Click on "Troubleshoot". Under Advanced options, click "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, remove DVD/ISO and then reboot the system. The server should now boot and present the logon screen. Press Windows Key + U. At the prompt you can change the password, by typing the following command: net user administrator Password123 This will set the password for the Administrator user to be Password123 (case sensitive). Now repeat the DVD/ISO boot steps and open command prompt above and run the following: c: cd Windows\System32 del Utilman.exe ren Utilman.exe.old Utilman.exe Done!