Windows 7 locking up

Our computer has started acting weird lately.  When you do a left click on the mouse to Firefox screen will get a circle that goes around and around and the screen gets like a partially  opaque mask over it.  Usually I have to X out of the Firefox page and restart it.  I have run Norton 360 and another program called Speedy Pro PC, but nothing seems to work.  Could it be cookies on my PC and how do you remove them?