Try uninstalling Norton AV and then reinstalling. If this fails try the helpline at Symantec. I had a similar problem once when I was using Norton 2002 on Windows 98, and the answer was a deletion of some files, but I cannot remember the details.
Fujitsu Lifebook P727 laptop review
Best of the Grad Shows 2017: University of the West of England (UWE)
Best value Mac: Which is the best £1249 Mac to buy
Les meilleures GoPro 2017