The solution is to hold down the power button and keep holding it down. For up to 1 minute. This does get results. And it says something about an unfinished software update. I press enter to say "go for it" and it continues. It seems to power off at least two times, but finally seems to be up and running showing my location. And now I can power it off normally.
Tom's backpacking pages / tom@mmto.org