Photos to Import Not Displaying

This problem just started.  Using LR 11.4 on Windows 10 PC.   Went to import raw files from memory card using card reader in my PC.   Something I have done hundreds of times.  Selected folder and subfolder but no photos are displayed in the grid or single format.   Just see blank black screen.   Typically use COPY AS DNG but tried COPY as well.  No difference.   This was working fine with same memory card 15 minutes earlier.   Have opened and closed LR as well as rebooted computer several times but same result.   LR will show me the files in Explorer and I can view photos using any other photo viewer.  This problem is occuring with any memory card or any drive on my computer.   I cannot view any photo to import.   Reviewed preference settings - did not find anyting unusual.   I have researched on Community and found similar problem from 2018 that was cured by selecting COPY vs ADD however in my situation, I was already trying to COPY AS DNG and ADD is blacked out so not even an option.