Can’t log in to the windows 2000 machine

I have a laptop that is on a domain at work. I brought it home to download backup work on my file server on my home network. I took the computer off the domain and put it in workgroup. Now I can’t log on at all. What steps did I miss, and barring never doing this again, how can you properly set a machine up from a domain to a workgroup and back again. Also can you change the administrator password in the windows 2k recovery console?