It's so difficult to explain what to do without being there.
Have you switched off router, modem and PC then seen if it's still the same when they are all back on.
Have you tried it in safe mode?
Do you have adaware, spyboy search and destroy or other similar tools and a decent antivirus to run in safe mode?
Then when you have fixed it get some advice on how to protect your PC in future and get into good habits rather than forgetting what you've been told until next time it happens, like most seem to!
eg, use firefox and get it to kill private data on exit...









