win xpfreeze on login

Hi,
Hope you can help..My co-worker has a Dell Dimension 4400 and when you click on a user account...It beeps once then freezes..If you strike control alt. delete it will then finish loading...He installed Microsoft antispyware beta and removed all its findings...Because it was starting to freeze during normal operation..I think he started to reinstall xp home and cancelled in the process..Is a format and reinstall the only option now?
Thank's ,
Chris...