Sys Resource Plague

Could someone please assist me in figuring out why my system resources are
constantly fluctuating from 0% - 25% every other second? Yes, I've already
looked at every program that is running and I have run Adaware and Spybot
looking for spyware. I have also ran Norton. The offending process that
is using the 25% is simply -System- according to Task Manager. Please
someone reply!