I helped a mate out with a similar problem not long ago. He was running way to many anti - this that and the other apps. One of his main system hogs was Spybot search & destroy. Its realtime protection was very resource heavy.
Look and see what teatimer.exe is using up in cpu. Thats the spybot real time protection.
Also svchost.exe, have you got automatic updates selected?
Did this occur shortly after a windows update?