Firstly, uninstall norton and throw it away because its rubbish! as your finding out!

I had similar problems when i had norton and one day it told me it had an error in the programme and it couldnt be fixed so i had to re-install it or something, needless to say i didnt bother what with everyone telling me to delete it!

So yeah uninstall norton completly and then im going to give you a couple of links to some VERY popular FREE anti-virus software and a firewall for good measure.
Anti-virus: http://free.grisoft.com/doc/1 (click on "New recommended program update (AVG 7.1.385)")
thats the lastest version of AVG, when you have installed it hit the "check for updates box".
Firewall: http://www.download.com/3000-2092-10039884.html

LOADS of people use these free programmes along with me for the last 6months and and im on the net everyday, pc is spot on

Im sure the other regular pc room bofins will back me up here in saying these are good pieces of software

P.s you will/should find your pc runs much better when you have uninstalled norton as its a BIG memory hogging programme!

Let us know how you get on matey