Several days ago computer starting freezing. It has increased in frequency to where is has now been happening at 1 minute intervals. The top of the page says "not responding" and the screen has a washed out appearance. I can see the page behind it. I tried downloading firefox 8 to see if it helped, it did not. I also ran a virus scan of my computer and it came up clean. I cleared my history, cookies, etc, too from my browser.