|High CPU usage due to too many programs open in the background.|
High CPU usage due to an infection that got past Norton.
System in need of maintenance (general cleaning out).
Possible memory errors.
Norton itself hogging resources.
Run Malwarebytes to check for an infection.
Do a disk clean up.
Clean out browser cookies, history, and temp internet files.
Do a disk defrag.
Use msconfig, Start tab and uncheck all except MS & antivirus program, apply and restart machine.
Run Memtest86 to test your memory.
Tell us if it is only one or two programs (like games or video editing, etc.).
Remove Norton and install something leaner and meaner like Avast (free version).
You have to be a little bit crazy to keep you from going insane.