Left Domain and now I can't log on

I must admit that I do not understand domains in windows . I removed several pieces of malware in a windows 2000 machine which was required to log on to a domain. He didn't want to belong to the domain or even access the net on this old machine so I went to the computer icon and right clicked to properties and then ID or some such and then clicked the radio button to go from a domain to a workgroup named workgroup.
Now of course on reboot the domain name is gone and instead of accessing windows directly it is prompting me for a password again which neither I nor the client knows. Am I out of luck or is there a way out of this?
Anyway to go back or rejoin the domain or enetr windows with out a long lost password?

 

You can rejoin the domain if you know the account that has permissions to do so.

to join a domain, the computer will have to be on the domains network obviously. right click on My Computer and click properties. Computer name tab. Click on the Change button. You'll see a workgroup option and a domain option. click domain and type in the domain name. Youll be prompted for a username and password that has permissions to join the computer to the domain, usually an admin has to do it. If that is the password you dont know, youll either have to change it in active directory or ask an admin.

 

Since you abandoned the domain you have to log on to the local account.
Administrator is usually available, unless the IT dept disabled local accounts.
You can try hacking out the password or resetting it. NT offline registry editor http://home.eunet.no/pnordahl/ntpasswd/ try it, or if you profecient enough to make a bart cd try http://www.kood.org/windows-password-renew/

You can go back to the domain if you have rights to join, which would probably mean a visit to IT to get it done.