Windows 10 Credentials no longer present.

[Windows Central Question]

It appears my upgrade to Win10 (from Win7) now has become corrupted. "Start menu and Cortana are no longer working" error message appear, saying "sign out". I can not longer run any programs, much less get to "msconfig.exe", "sfc /scannow", or even DISM. I have no Internet Explorer" or (or other browser) access, and have tried 3 times to have Microsofts Windows Tech Support talk me through a solution without resolution.