Are you running virus protection?
Have you updated your DAT files, and done a full system scan?
If you have no virus protection, do an online scan:
http://www.pandasoftware.com/activescan/com/activescan_principal.htm
http://www.ravantivirus.com/scan/
.... and get virus protection.
If you don't find that a virus is your problem, check your system for malware:
AdAware - http://www.lavasoftusa.com/support/download/
SpyBot - http://www.safer-networking.org/index.php?page=mirrors
Install, Update and Run both. Remove whatever it finds.
Let the techs check it after that, so go get:
Hijack This - http://www.spywareinfo.com/~merijn/files/HijackThis.exe
Install, Run and post your log here for assessment.