Temporary fix found. Thank you to posters here for their advice. Who would have thought that a careless error by a peripheral manufacturer could leave me with an unusable computer..? I can accept (sort of) that they might make a mistake that rendered their own device unusable, but the impact of their error here was much wider/deeper. Whatever they were doing should have been tested properly.
No more HP products for my family.
No more HP products for my family.