McAffee is the worse thing about not detecting viruses. And everyone is correct you need to run a Spyware program to empty out all of the nasties that might be there.
My computers (3) are set up like Fort Knox and there is no way they will be hacked into, my buddy has tried so many times, to test my system. Go get these programs they are free and will fix any issues that you might have. The worse case scenario you will have to wipe the HD clean and start over.
Go here
http://download.cnet.com/windows/
In the search bar type in Avast and get their anti virus, then type in COMODO and get their firewall, then type in Spyware Terminator and get the spyware program. (this is a real time program so you know if something is trying to get into your computer), then type in CCleaner and get that program. This is the one that you need to get and run immediately. It can also repair your registry which could help a lot with the situation that you are having now.
I know this is a lot to comprehend but it will help you out in the long run. Oh and put Firefox back on your computer, IE is bad news.
All of these programs are free and are the best on the market.
Billy