OK, guess what. I did this. (I had to completely run down the battery for the computer to actually turn off).

Then I plugged in, placed the USB stick in its cradle, switched on and pressed F12. And, yes, the BIOS menu came up, and asked me did I want to boot from installed windows boot manager, from USB, or from one other choice I do not remember. Of course, I clicked on "USB" as a choice...

But then...

I got a message saying "this action is blocked because of current security settings" with exactly one clickable action which was < OK >. Grrrrr!

I clicked ok and found myself back in windows.

It seems the programme has figured out how to protect itself from being replaced!

I need a new plan!