scan your computer for spyware here http://www.doxdesk.com/parasite/ or http://www.pestscan.com/
Run http://www.safer-networking.org/en/mirrors/index.html spybot

You would need to do a msconfig to get rid of the offending program http://www.fixyourwindows.com/windowsxpsolutions.htm
1) The Alternatives Browser's 2) Installing Windows 3) Must Have Security Software! 4) Stop Popup's 5) Spyware Prevention 6) Removing Sasser from your computer 7) Removing Spyware and Spyware Provention 8) Using Internet Explorer Safely! 9) Web sites that test your firewall for free
http://computerhelphow-tos.blogspot.com/