Lauchlan, AVG & Norton together on the same system is a No No!.. Have a look @ this article (http://avgclick.me/prepareforAVGinstall).
AVG Guru
Lauchlan, Also just in case there are any Norton remnants left after the uninstall download & run the Norton removal tool (https://support.norton.com/sp/en/uk/home/current/solutions/kb20080710133834EN_EndUserProfile_en_us).
AVG Guru
It seems like main functions (welcome page, emails) stalled (falied to open) after Norton was installed 2 weeks after AVG installed. In past both had worked well together.
Lauchlan, AVG & Norton together on the same system is a No No!.. Have a look @ this article (http://avgclick.me/prepareforAVGinstall).
AVG Guru