critical error

after being unable to use my desktop pc for over a month due to it not recognising my password which was authentic, I finally took it to a repair shop and had it restored to windows 8:1 . Foolishly I decided to give W10 another try , every thing was fine for a couple of weeks , but when I logged on a couple of days ago I was confronted with the following message , Critical Error , Cortana and Start Menu not working We'll try to fix it next time you log in . Log Out. I logged out and it restarted but came up with the same message. Outcome is I cant access the internet or anything which is internet suported , cant use the start menu, but can access some downladed apps which are on the desktop and don't rely on internet connection. has anyone encountered this problem , did you manage to fix and how ? dockerdooley .