I would make sure that you have a virus scanner and its up to date. Do a full scan.
I would then run a spyware removal utility on it such as Spyware - Search and Destroy:
http://download.com.com/3000-2144-10...ml?tag=lst-0-1
Make sure you clean all the spyware off it.
that should fix your prob.. you can also try looking in your hosts file for any wierd entries (the spy where software will do it for you)