I initially searched and posted on a Screen/Writing problem. I have since revised my search and found the following link (among others) that describe my problem completely -- 1 inch dead strip down the middle of the tablet.
Apparently, it's a digitizer connection/seating problem identified with older Motion tablets. I followed one of the home remedies and it worked, temporarily. I took two cleaning cloths and pressed on each side of the screen, gently, but firmly, as if re-seating the digitizer from the outside in. It regained all functionality in both tablet and notebook mode for about two minutes and then the dead stripped returned.
So I'm posting this in the Gateway forum in case anyone else experiences the same thing and wants some more info.