My computer constantly freezes for about 2 seconds. This happens EVERYTIME I move the mouse.?

I have bought Norton 360. I have ran scans for adware, spyware, malware and viruses. I have even doubled the memory on the computer (as much as the motherboard can handle). Everytime I move the mouse or hit enter on a website to load another site, it always freezes for about 2 seconds. When I move the mouse again it freezes. If for some reason it won’t freeze, it will run VERY slow. The sytem is about 6 months old and has Vista. It has only started doing this recently. I restored the system to it’s earliest point and nothing changes it. HELP!
Only about half of the hard drive is used.

Checking the temperature of the Case.
Open case and look how does CPU fan Work normally or not?
Because when you load web site the CPU is operated hardly so it will increase the temperature of CPU , up to an limitation,the CPU can’t stand Anymore and It will hang you system.

Spybot-Search and destroy(TIME of scan 32 minutes)