Norton is not capable of finding the culprits in your system.
Download a good AV program (Kaspersky 5.0 trial version www.kaspersky.com)
Run the updates, scan your pc, it WILL find the trojans on your HDD.
Next: Download SpyBot Search and Destroy:
http://www.download.com/3000-2144-10122137.html?part=104443&subj=dlpage&tag=button
Run the updates, scan your HDD, it will remove the registry entries.
I had the same issues going on, the above cleared it up & kept me from formatting.
JR