I'm sorry, but I think you will need to contact T-Mobile for support. Call them from another phone at 1-800-T-Mobile.
If you don't care much about the info on the phone, then do a hard reset to factory defaults.

http://www.hard-reset.com/htc-hd2-leo-hard-reset.html

CAUTION - DOING A HARD RESET, YOU WILL LOSE EVERYTHING ON YOUR PHONE. REMOVE THE MEMORY CARD BEFORE DOING A HARD RESET.

Good Luck,
Mark