Where do I start??

I am using my daughter's laptop because my machine is seemingly kaput. My son was using it earlier and must have gotten some b-a-d virus (OR I installed some printer software yesterday...but I don't think that's it). ANYWAY, I cannot get on the p.c. (Windows XP) to do anything. After startup, you get the desktop background, but no task bar, no icons, no nothing. If you start it in safe mode or with the system disc inserted, you get the screen where you can pick which user account to use (Admin or me), and neither will load. It just flashes, says "saving user settings" and that's it. WHERE OR WHERE do I start?
I've used you guys twice before, and I know if anyone can help, it's you. Yes, I had anti-virus stuff installed per your recommendations...don't know WHAT he did!
Thanks