When I setup TFS for the first time, I usually use the TFSSetup account, and with this account going to login for the first time.
How to login as a differen
Another approach you can take that worked for me, was to log into the web interface for TFS, then use that to log in as another user. So, navigate to:
http://yourtfshost:8080/collection/web/
(or whatever your web address is)..
Then, click on your name in the corner and select "sign in as a different user."
Essentially, this does the same thing as the above suggestions. It simply replaces your credentials in credential manager with the correct ones.