OK. Figured it out.
I discovered my own answer: Apparently I minimized
the Illustrator window inadvertently. I'm a Mac person who is now working on a Windows PC custom built quad computer. I'm still wreaking havoc by just being unfamiliar with the UI. Anyway when I right clicked the app icon at bottom of window, hit maximize and there was the artboard. I opened the file and all was well. If I wasn't so happy I would have been embarrassed.
Lesson? Return to the basics occasionally. It's often something simple that goes wrong.
Thanks to those who responded.
You are welcome, Julian.
On behalf of all.