messenger nightmare, please help

a friend used my computer, she has hotmail, claims she NEVER downloaded
anything. Somehow, my computers windows messenger picked up HER info. Now I
can do NOTHING with the messenger. I can't delete it, can't change the
personal info to mine. Add remove programs doesn't pick it up to remove it.
Can anyone just help me get this off my hard drive? I have all sorts of web
pages and stuff that have picked up her info. It's like its not even my
computer anymore. its become its own virus. Thanks
.