Bob, I wrote it above - The deinstall routine from your "clean install" link pimped the Windows boot manager which now alsways starts in safe mode.
Which means Restricted services and minimal screen resolution. And as this is injected inside the boot code this works permanent.
As most people I have problems here & there in the past, but this tops all of them: not even back to a clean system image solves the problem.
End of my relationship with Avast.