How to prevent an automatic logoff

A friend has installed PC-Cillin on an XP Home machine and now when he logs on, the machine runs through the logon process then automatically logs off without any intervention by himself. We have tried logging on as Administrator and using Safe mode but cannot prevent the logoff procedure from running.

We could probably access the hard drive from a network and I wondered if I could rename the .exe file that runs logoff to interupt the process.

Does anyone know the name of the file or can perhaps suggest another way of dealing with it?

Thanks

 

I've successfully dealt with the "endless boot loop" by following the instructions on this page and/or running chkdsk /r from the Recovery Console. Which I try first depends on which I think of first.