Did you do the recent HP update via Apple Software update? Came through this past week.
Thank you, Robert.... good idea; I'm dreadful about staying on top of updates. But I finally discovered a simple problem. I'd checked that all my cables were securely in.... except for one... the connection to the Belkin hub. Must have gotten dislodged when I was cleaning recently.
That's what I get for cleaning. Thanks very much again for responding,
louise