Norton Security Suite will NOT stop running, slowing down computer.

Hi,

I recently noticed that my computer has been running really slow.  Specifically, the hard drive activity light is constantly on, and I can hear the drive heads "clicking."  My computer has noticeably slowed down (ie, longer to bring up programs, programs freeze, Norton GUI freezes).  Upon checking the Norton Performance, I noticed that Norton was using a good 90% of the CPU in use at the time (ccsvchst.exe 18%, total ~CPU 20%).  Under Norton Tasks though, NOTHING was listed as currently running, which is strange since CLEARLY Norton is doing something.  Turning on Silent Mode has no effect on decreasing CPU usage.  I used to run NIS 11, and I never had problems with Norton slowing my system.  A full system scan a couple of days ago came up clean, and no changes to the computer have been made since then.