Thanks for your help here. Unfortunately neither the reset via automatic repair nor the recovery of Windows via USB worked.
The reset itself worked but when going through the Windows set up process I had the same problems as encountered previously, although I did get a fair way through the process the first time after the reset.
I created a USB recovery drive as you recommended. There were two versions to choose from, 21H2 and 22H2 so I actually created two drives but when extracting the 22H2 version there were two CRC errors (in files install.swm and install2.swm)** so I used the 21H2 version. The installation started ok and completed 'Readying Devices'* but then the machine went dead when 'Readying'* (only the cooling fan was running but eventually stopped). It did not respond to the power-on key but eventually, by holding it down for a long time, I got a black screen with white windows logo followed by some activity ending with an 'Install Windows' message saying
"Windows could not complete the installation. To install Windows on this computer restart the installation."
I tried repeating the Windows installation form the USB drive but the result was exactly the same. That's as far as I could go.
I noticed that the directions for creating the flash recovery drive were slightly different on the MS Web site to those you provided (the site says to use a Recovery application where you just say to copy the files). I did as you said which made sense and seemed to work ok.
My conclusion is that I still have a hardware problem. Two machines in a row seems odd. I assume my power supply is not glitching the machine since I had issues even before I connected it. (It's the original MS 102W charger.).
*from memory. I am not certain of exact wording.
** Someone at Microsoft should really fix that I think.