Windows Stops Working


Sep 11, 2011
My desktop computer build with Windows 8.1 for an OS has been running without flaw for several months, but lately (within the last month or so) I started getting a Windows pop-up saying that "Windows has stopped working and needs to close the program". This happens regardless as to what program I am running (except for my Firefox Browser).
I have been using the same [updated yearly] Norton 'Internet Security' program I have used for several years, have completely cleaned my system using Norton 'Utilities', and have kept everything updated with the latest applicable software.
My question for the community is whether this Windows pop-up is being used as an incentive to upgrade to Windows 10? Perhaps a type of 'NAG-ware'?