Sorry to report none of the FAQ's remarks applied to my situation.
Something wrong with installer file, b/c, previous version of DO Pro was re--installed sucessfully.
Besides, that is not the issue at hand, although installing a newer version was a proposed option.
Never-the-less, something changed, somewhere, within my system, specifically, that directly impacted the way DO Pro handles the double-click to open video files.
I'm blaming DO Pro, I really like the software very much and had a couple of years of flawless performance up until recently.
However, if this can't be resolved I will have to move to another software program such as XYplorer which thus far has been a suitable replacement to DO pro during this interim.
I hope there is a final solution soon.
Thank you thus far for all your support efforts.