It is not surprising to receive the critically low battery message , after draining the battery.
I know you were trying your best, but that was unlikely to achieve anything

I have little doubt that part of your problem is Norton, that is NOT to single out Norton. However the unquestionable evidence is that many if not all, third party Antivirus programs do not sit well with 10. They are OK at the start and then invariably produce problems, after major security updates to Windows and especially after version updates.

however to return to the issue at hand, it is often caused by shutting down whilst updates are in progress. It can however, also be caused by other third party software.
System cleaners, registry cleaner, boosters and the genre of - make it go faster programs are often to blame.

I suggest you start with a forced boot to recovery
That is power on
wait for the System event notification
power off
repeat three times
All being well your system will automatically load
Windows 10 options for recovery

power on the pc - power it off (by holding down the power button) while windows is still starting - repeat 3 times, then windows will recognize it as "boot failure" and go to the repair screen" ..

This will work if it commences the load of windows BEFORE the system event notification
You power OFF on the spinning circle for the commencement of the windows load.

If that DOES NOT work, when you reply I will offer other options

 

Thank you very much indeed for your advice.

I am at the "Chose an option" menu with (1) Continue to Windows, (2) Turn off, (3) Troubleshoot.

The "Troubleshoot" menu has (3.1) restart PC, (3.2) advanced options, (3.3) turn off.

"Advanced options" has (3.2.1) startup repair - fix problems that keep Windows from starting, (3.2.2) uninstall updates, (3.2.3) change Windows startup behaviour, (3.2.4) change UEFI settings, (3.2.5) go to command prompt, and (3.2.6) use a system restore point.

Which of these many options should I choose, and what should I do then?

Thank you again!

 

It is difficult to know what to try, not knowing what exactly did cause the issue

I suggest you try first startup repair

If it fails to repair on the screen that shows that message click advanced options and run it three times
as here
Run Startup Repair again:
Click/tap on Advanced options, and go to step 2 above. Sometimes it may take running Startup Repair up to 3 times and restarting the PC each time to fix the startup issue.

May I add - thank you to YOU for being appreciative

 

Startup Repair said it could not fix the problem, but on the first reboot Windows started normally. Thank you!

In retrospect, the cause may have been that my problem occurred when I had internet access via bluetooth tethering to my smartphone in an place with poor reception - it's possible that the computer lost internet access at an inopportune moment. After Startup Repair, Windows said there are updates available, so I've downloaded and installed the Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 1903, Windows 10 version 1909, and the 1909 update KB4535996 - and the computer now restarts normally.

Are there any other remedial actions I should take?

Thank you, again, for your help. It's *wonderful* that you're prepared to offer such helpful advice to strangers - it's one of the many features of the internet that show the best side of humanity.

I've made a donation to Tech Support Guy.

 

If everything IS Ok and all is working you are good to go
It was in view of your last post - a loss of connection I think during the installation of an update
If you use internet access via Bluetooth tethering again
PAUSE updates as here
https://support.microsoft.com/en-gb/help/4028233/windows-10-manage-updates

Pleased to have helped and although you will have received a thanks from the site for your donation, which as you probably read goes to

All donated money will be used to pay for computer hardware, the Internet connection, server software, and other fees that apply directly to running the site.

On behalf of the site owner
Mike Cermak
"TechGuy"

Thank you

 

Thank you. I will definitely pause updates in future when I'm tethering.

 

Indeed. Thank you for the kind donation. We appreciate it very much.