Critical Error: Start menu and Cortana aren't working. We'll try to fix this for you the next time you sign in. /avast

Sorry don't know where else to post. Lot of bloviating. There are probably a lot of reasons for this dumb message and the messages are similar. Good argument for better messaging. What seems to be happening in my case is that Avast, what do you want, it's free, is pushing out a software upgrade for windows 10 using its windows 7 program. This breaks everything better than a virus could.  If you can bring up Avast there will be a message that a program upgrade is waiting in the software updates section, pushing that through, restarting each time it asked, fixed it for me.

Then it broke again. Guessing Avast is trying to tell me something, perhaps pay them. Uninstalled Avast then things worked again. Avast sent me a very nice email explaining how to uninstall. If you don't want their web service then troubleshoot program(right click) gets you to control panel. Hello defender.