Computer has suddenly become slow to bring up pages, sometime does nothing

The computer is only a few years old and was the fast reliable one in the house. Sometime after a scan by PC tools, which I did regularily, it became slow to respond in bringing up pages. The little blue circle would just spin on the screen. If you were on a page and hit a link, it again would be slow or not even respond to that click of the link. AVG shows no viruses, Malware Bytes Anti -Malware shows nothing, I've defragged and run CC Cleaner and it doesn't seem any better. I also did a system restore to before that last scan. It's an HP with AMD Athlon running windows 7 with 4.0 GB of RAM. Thanks