Need computer help please?

ok so starting today my computer's CPU speed keeps going really high locking my computer and then going back down......it's been doing this all day. i have antivirus and am sure there are NO Trojans or viruses, believe me i know. all running processes were check and all of them are supposed to be running, and it doesn' do this when i'm disconnected from the net, idk what to do, and it is only a little better when i am not on the Internet, it is still messed up though

READ THE QUESTION BEFORE ANSWERING OR I WILL DELETE AND REPORT YOUR ANSWER, PLEASE AND THANK YOU

* 18 minutes ago

* - 3 days left to answer.

Additional Details

10 minutes ago

i know it is NOT malware, i know.

and i have tried restarting, and have full protection

7 minutes ago

there is no reason for this happening

i have a new Vista computer with 2 Gigs of RAM

4 minutes ago

i even shutdown my antivirus and software firewall and it was still doing this

Need computer help please?virus protection

Where to start?

"READ THE QUESTION BEFORE ANSWERING OR I WILL DELETE AND REPORT YOUR ANSWER, PLEASE AND THANK YOU" - All i can say is Shutup.

Secondly

"i have antivirus and am sure there are NO Trojans or viruses, believe me i know" - In the unlikely event that your correct (which i highly doubt) then its a system error