First you want to start your computer in safe mode (I say that a lot :D).
Repeatedly strike the f8 key while your computer is booting up and select "Safe mode with networking"
Once Safe mode loads, try opening up internet explorer. Head to http://housecall.trendmicro.com and run their spyware/virus utility. Keep running it until it displays no results.
Also try download spybot and adaware. Update those programs and run them both until they don't find anything.
Also head to http://www.trendmicro.com/spyware-scan/
and run that utility.
Another option is physically removing the hard drive, hooking up to another computer as a secondary drive and running a virus scan on it. That requires some expertise.