Hi Ulf,
Hoorah! I did as you said, and once I restarted the computer, it now has sound! (The reboot was necessary, for your future reference; it didn’t work before I did that.)
Thanks ever so much, you and Daniel have been most helpful.
Just one last thing - I still have to go to “playback templates” and select the template every time I start up the program. Is there a way to make it default to being selected?
E.
Try setting the default playback template in Edit / Preferences / Play.
The default setting should be HSSE + HSO for Dorico Pro and HSSE for Dorico Elements.
If it is already set, try changing it to “Silence”, click “apply”, and then change it back to what you want.
That worked, thanks Rob!
I can now get on with learning the program. 
All the help is much appreciated!
Hi Elenmirie, glad to hear that. And see, I told you, sooner or later we’ll get you up and running. Voila 
You did indeed.
If there’s anything further I can do to help you track down whatever prevented the smooth installation of my shiny new software, please let me know!
One really does expect that if one installs with the defaults, one will end up with something that works. 
Thanks for all your help!