Have you updated your virus definitions and run a scan over your entire system?
Other times when I've heard of a complaint like yours is been because there is a virus infecting their computer. If you don't have a good antivirus program (what the heck are you doing going on the internet without one!) try installing a good freeware antivirus like AVG from Grisoft: AVG Anti-Virus and Internet Security - Download AVG Trial Versions for Free let it scan your entire system and then see of you still have the same problems.