The title's misleading but I couldn't find a way to express it succinctly.
If I have 2 Excel windows open, with one or more workbooks within each
window, and I click on an Excel file-name in Windows Explorer or on a
shortcut to an Excel file-name, nothing happens. If I close both Excel
windows and try it, the file will open. Or if I go to Files, Open, and
Browse to the file name it will open. This is both new and a pain in the
rear. As recently as 3 months ago I could open six or eight Excel files at
the blink of an eye, from Windows Explorer or from shortcuts. What changed?
How can I change it back to the way it was?

Thanks "ConfusdNHouston"