Very simple. Norton products these days are total garbage. So, do this:
1) Download AVG Free:
http://free.avg.com/gb-en/homepage, but don't install it yet.
2) Disconnect your computer from the Internet, either by unplugging the its network cable or by switching off your wi-fi network...
3) Uninstall Norton. HOWEVER, be fully prepared for the fact that you may not be able to uninstall it completely. Norton products are infamous for being next to impossible to get rid of...
4) Still disconnected from the Internet, install AVG which you downloaded earlier. Ignore its nagging that it can't update itself because it can't find an Internet connection.
5) Once it's installed, and still disconnected from the Internet, allow AVG to perform a *COMPLETE* scan of your machine. If it finds anything on your machine which it thinks shouldn't be there, do whatever it suggests in order to remove it.
6) After the scan is complete, connect back to the Internet and reboot the machine.
7) Go into AVG, click Tools, Update and allow AVG to update itself.
8) Do a Windows update.