Problem logging on to Windows

I have a user who is trying to log on to his Windows XP machine. When he puts in his username and password and clicks on ok, his PC just freezes. I had him try to log on as the administrator and the same thing happens. I had him run a hard drive test and it came back fine. I then had him boot into safe mode and try logging on as himself and the administrator and the PC froze up both times. I then had him try to start the PC using Last Known Good but when it came back to the login screen, an error message popped up which said "One of the files containing the system's registry data had to be recovered by use of a log or alternate copy. The recovery was sucessful.". He clicked on OK and the PC froze again.

Can anyone think of any reason this may be happening and how to get around it? I really don't want to re-install the OS if I don't need to, but that is the only thing I can think to do at this point.

Any help would be appreciated.

Cheers
Rick