I think Microsoft Windows 10 updates are cowboy style! why you ask? Because the start icon F-ups and the message “Critical Error/Your Start Menu isn’t working. We’ll try to fix it the next time you sign in.” You may also see the error, “Critical Error/Start menu and Cortana aren’t working. We’ll try to fix it the next time you sign in.” The Microsoft Answers forum main thread for this problem is currently up to 73 pages, with 1,195 people chiming in that they’ve had the problem, too.
Short answer: Microsoft still hasn’t figured it out. Microsoft engineer Paul Sey says:
You may be able to temporarily resolve the issue by booting to Safe Mode, and then immediately booting back into normal mode. This workaround may resolve your problem for a while, however the error may return later.
Meanwhile you can't access your apps..One work around is to reinstall W10. It save your files but you got to reload your non-microsoft apps manually..are you kidding? Used to be with W7 you could fix your OS and save everything but not anymore.