Norton has long had a rep of being a resource pig.
Get rid of it, they must make most of their sales on pre-installs.
I use System Suite Pro 9.0 by Avanquest, Boost Speed by Auslogics, HostMan, Win Patrol and Task Catcher. (google 'em)
If I fear an uncaught virus with SSP9, I run AVG's antivirus, and keep track of actually messed up or trojan files, and then use a boot CD that gives me a DOS prompt and manually toast the offending files.
SSP9 will quarantine automatically offending files, if known to trigger falsely you can whitelist the file so it ignores it. The quarantine will tell you the threat level and what it thinks the file has (trojan or specific virus).
SSP9 has it's superior (to Windows built in) firewall, active protection against viruses and bad links, checks SMTP/POP3 email/attachments, and a ton of other useful utils in it, cost is around $50. (sold at Walmart or get direct)
Avanquest might even have a trial so you can test it, all the others have a trial that I listed, except freeware HostMan 8) WinPatrol you pay for access to his file info base, and never an upgrade fee.
BillP is da man, LOL! (he makes Task Catcher as well as has a good blog on his site)
Enough rambling, check'em out!
Oh yeah, I am running XP still, if it matters, I will not be playing with M$'s sad excuses for upgrades anytime soon.
PS. Try Spybot and Spyware Blaster, almost forgot about those.