Through the Windows Task Manager, my CPU Usage History is jumping like crazy. When I go to the Process tab, I can see a few processes starting and disappering so fast I can't even right click any of them to check it or even end its process. All I know that there are 4 processes starting and disappearing rapidly and the names of these process start with an "S". How I know that is cuz I sorted the processes by name and it is before the System process and after the svhost process I don't think it's a virus cuz Norton didn't detect anything

How can I stop this????

Try Ad-aware or spybot , they will find any unauthorised apps running on your system & eliminate them.

If you are using XP or W2K set up some system logging to see if anyone is in your PC. Control Panel>Performance and Maintenance>Admin Tools>Event Viewer. This lists all sorts of things that are going on. Application gives you a brief overview of what has been accessed program wise for the duration of your session. Security and Session do similar things if you have them set up.
You should also password protect your drives, and set a local security policy in Local Security, also in Admin tools. Make sure your firewall is on and think about something like Zone Alarm to boost it.