Gray screen during screen share

I've used Zoom a lot to teach college chemistry and didn't have this problem before, but today when I did share screen my students only saw a gray screen with my image in the corner, or a black screen only, no matter what window I tried to share with them.  None of my changing of share screen menu settings (TCP, acceleration, screen capture) made any difference.  Restarting the computer (Windows 10) didn't fix anything.  All I had done differently was I reloaded Zoom Client to make sure I had the latest version.