Here are some steps that will help in resetting your password:

Instructions

To reset the password on your Windows 2012 server, simply complete the following steps:

Closing the command prompt, you should now be able to log back onto the server using the password you have provided in the last step.

Cleanup Steps

Once you have verified you can log on to the server you will have repeat the steps above and boot using the Windows Server 2008 DVD/ISO and run the command prompt again.

You should be back up and running as if nothing ever happened.