Hi BD,
Appreciate your interest.
When the problem started both the Display and Computer were set on 15 min.
Since then, trying to correct it, have tried various combinations.
Nothing solved the problem so for several days I went thru process of shutting down/restarting many times.
These are the current settings. It's working i.e. my Display screen stays on. (But I know it's not ideal solution).
Both Computer and Display are set to Never Sleep.
Put the hard disk to sleep whenever possible is checked.
Also checked is Wake for Network Access and Allow Power Button to put Computer to Sleep.
The problem started about 2 weeks ago when we had two power outages on the same day - so that might be a factor or simply coincidental.