First I would open control panel, network and sharing centre, bottom left click on internet options, connections, lan settings and untick 'use a proxy server...' if it's ticked. See if you can download AdwCleaner from here. Run that and delete all it finds and let the PC reboot. Now see if you can run Norton on a full scan.
Also run the free version of Malwarebytes, scroll down and select the free tab , update and run a full scan after running Norton.