xp start up problem

I built a computer for a "friend", checked it all out and everything was running perfectly.
He takes it home, says all he did was update xp to sp3.
Now, when the computer is turned on, it will load to the log in screen with the users names shown. You click on the name, and it will display "loading user settings", then immediatly show "saving user settings". Then it's back to the log in screen.
I tried starting in safe mode, but it is the same thing.
Luckily, I had another hard drive handy to put in the computer, but now I'm stuck with one that is junk, at the moment.
I have temporarily installed this hard drive in an older machine I have, and still the same boot issue.
I'm guessing that along with sp3, he picked up a virus. If so, do you have any idea which one, and how would I get it cleaned?
Thank you so much for your help.

 

Lots of problems installing SP3, glad I did not run into any of them. Seems anything from anti virus software to AMD processor hardware can cause them. First thing I would try is using nlite to slipstream SP3 to a new installation disk and then reinstall, while at the same time getting rid of some of the XP software I never use. I imagine your Windows disk already has SP2 so slipstreaming that won't be necessary. Or you could try installing Windows and update SP2 and or SP3 before doing anything else. Both service packs are available from Microsoft as a download so you won't even need to be online to install the service packs. If there are files or programs you need you could try using the master HDD with the problem as a slave and copy files, installers, drivers from the disk that way. Imagine Last Known did not work either. You could also try using the Recovery Console to remove SP3, instructions are here, among other places:
http://aumha.net/viewtopic.php?f=62&t=33246
Hope you find an amicable solution...
Bug