Changed domain to workgroup but no local users

I was trying to network 2 computers one was  a new computer and the other was a computer that was set up by a company that is no longer around.  The old computer was set to a domain, so I could not network them together to share the files.  I removed the old computer from the Domain and put it on a Workgroup and then restarted the computer.  The problem I have now is that there is no way to log into the computer because all of the local users including administrator have been disabled.  Is there a way from ubuntu, or some other boot disk to re-enable one of the local users so that I can get back on the computer?