Is Norton part of the supplied set up and
do you have the program disk?
Is Norton is a software you have purchased separately and you do have a disk
If you can answer yes to either of these then the answer is to uninstall Norton to see if the machine will run clean.
If Norton is a 'builtin' feature and you have no disk then you have to contact Dell before you remove it .
Removing a given program and re installing one by one is the only way to reveal a duff install.
It helps of course if you have all the disks.