OK, I found the wired keyboard. It was where I looked for it first, but it had fallen behind some of the other things on the shelf.
It's a ThinkPad keyboard, it works perfectly and even the 'eraser head' works (which will keep me from reaching the mouse).
I didn't install any new drivers, just plugged it in and used.
So I think the evidence is that my 'built in' keyboard is probably failing.
It's an old ThinkPad computer that used to run Windows 8 and I upgraded as soon as Win10 offered the free upgrade. I use it basically as a recording device. I do MIDI work on my main computer, send the MIDI to 7 synth modules. The audio outputs go through a mixer to the old computer.
I find using two computers a lot easier than playing and recording on the same computer. I can have the play and the record controls and screens up, visible, and working at the same time.
So, I'm thinking of just using the wired keyboard rather than spending time on repairing the old computer. Lenovo doesn't seem to have a replacement on their site, Amazon has a compatible one by Autens for $42 (perhaps shipping?) and it might take the better part of a day to replace the keyboard. If I find using the wired keyboard to be too much of a hassle, I'll take that route.
Thanks again for your generous help and advice.
Notes ♫