Domain name is invalid or doesn’t exist

I have a single domain controller on my Windows 2000 network. When I try to add a computer to the domain, I get the following message, “The domain name “xxxx.com” is either invalid or does not exist”. I recently lost my SYSVOL share, but now with MS’s help, have it restored, however, my original problem still exists. I can’t add computers or servers to the current domain.