Started 10th August 2020
At the start of August 2020 Windows Update insisted on doing an update, the update failed, Windows undid it and I was left with a computer with a blank screen plus mouse pointer.
I found that Ctrl+Alt+Del gave me a screen with various options, like "Switch User". One option is Task Manager and from this one can run commands. I ran "cmd.exe" and then "sfc /scannow" which fixes damaged system files, after this the computer went back to working as normal.
Getting to the above point took me a couple of days. The fact that the computer was alive except for the user desktop gave me hope.
From the Ctrl+Alt+Del screen there is a power off button and holding down Shift whilst clicking on it results in the next boot going into a set of repair options. This gave an error message about "evbda.sys", searching for how to fix that eventually gave me the clue to use the sfc tool but no options other than reinstall Windows. Similarly three failed boots in a row (power on, let it start to boot, power off) which should give repair options ended up with the same error screen.
Booting from the Windows 10 installation media (a free download from Microsoft) only offered a complete reinstall.
I would have liked to roll back to when the system was last working, but that option was not available (see above - no repair options). I did not investigate if there was a command line to do this. Another idea was to create a new user (who might have a working desktop), that can be done from the command line, and it was not a solution.
The idea to use sfc came from 5 solutions to fix evbda.sys errors on Windows 10.
There was a build up to this. A big Windows update which hung prompted by "Your Version of Windows 10 is nearing the end of service. Restart and install the most recent version of Windows" (Feature update to Windows 10, version 1903). Following my own previous experience I turned off USB 3 support in the BIOS and the next day the upgrade appeared to have succeeded. I am not so sure because I didn't look and it is common for updates to fail and then undo themselves.
I have an ASUS P8Z77-V motherboard, only the basic version.
To get the Windows update log files use the command
I am now sat here with the same tempting upgrade message from Windows, what am I going to do...