Since upgrading to Windows 10 I was having trouble opening my Norton Security and running scans. Did a bit of Googling and found that the Norton official advice was to download the uninstall tool and uninstall/reinstall. I did this a couple of times but the problem soon returned. Then I remembered I had the same problem initially with Windows 8.1 and found the answer was to switch off "fast start up" in the Power options. Apparently Norton requires everything to be switched off when you shut down but having "fast start up" checked leaves some programmes running. So I switched off "fast start up" and now everything seems to be working OK. Surprised Norton themselves do not give this advice rather than uninstalling etc.