do you use any anti-bloatware programs like Ad-Aware or Spybot? If not, you might want to download and use one of them, sounds to me like you have gotten your web browser jacked. I recommend the ad-aware because its easy and doesnt screw with stuff that might mess up your computer. It deep scans your registry and hard drive for crap-ware and gets rid of it safely, where Spybot is more of a experienced windows user program that will delete stuff that could harm your boot up process if not set correctly.
~wnied~