I think you might have some traces of the trojan/virii still left in your system. IMO, uninstall norton first. Get avast or pandora or pccillin. Install , update and scan with them. If you can do an online scan,here is the link
Clear unwanted start up entries in the msconfig menu. (start->run->msconfig , startup)
*also get spybot and adaware to clean up the mess left by your internet.
If your problem is not solved, download 'Hijackthis' , run it and post a log in the 'Hijacklog analysis' forum in 'virii' section.