Adding to a domain

Optiplex 745, Windows XP;

While adding computers to a domain, I received the message that the name given was already in use.  Spoke to the admin and he suggested that I take it off the domain put it in a workgroup, restart and then put it back on the domain, which I did.  Although it was accepted in the domain under the name, I can only log into the computer as a workstation.  What must I do to be able to log into the domain as an administrator.

Another name is not an option.