I'm finding that firewalls can play havoc with PC performance and the web especially if you have more than one. I disabled Avast's and Malaware's and I just use MS Security Essentials for real-time protection. You might uninstall Norton and reinstall.
I had CA once, but don't anymore. That should say something.
PC Essentials -- despite it being a MS product, I have and think is great. Because who knows more about attacks against its own product than MicroSofty? lol
BUT NORTON SUCKS THE BIG ONE! GET RID OF IT -- I CONSIDER IT WORSE THAT ANY VIRUS!! Seriously.
Did I say that outloud?