Reason I asked is I had a problem like this a while ago, and it wasn't a virus as such, but a pretty malicious spyware problem.

I got a dodgy desktop backround (it was just blank with a web URL on it) but my IE was hijacked and the home page reset, and I couldn't change it no matter how hard I tried.

I ended up going to this forum : www.d-a-l.com who talked me through everything supplied the links for the programmes I needed to run and generally solved my problem for me - superb forum with superb users!

Anyway, first of all, just install and run both Ad-Aware and Spybot (links in my first post) and see how that goes for you.