I would try running a virus scan and an adware/spyware scan to see if there is anything bad on your computer. Try using AVG antivirus (it's free and works great). You can also try Avast! antivirus (also free). They both do great at finding and removing viruses and they don't use really any system memory. If you want to remove spyware try getting spybot search and destroy.
Here's the link to AVG antivirus: http://free.grisoft.com/doc/avg-anti.../lng/us/tpl/v5
Here's the link to Avast! antivirus:
Here's the link to Spybot Dearch and Destroy:
Another program that's good to use is the online scanner that PC Cillin offers for free. Just go to this link and use it, I've heard people say it does a great job but i've never used it before: http://housecall.trendmicro.com/
Hope that helps and if you're still having problems let me know,