"No photos in selected folder"

I've read the same problem and solutions that others have followed, but can't seem to fix it in my application.  Yesterday, I imported over 1700 pictures from an event I just shot.  My LrC was running extremely slow and while I tried to do a back up before closing the application (closed it so that maybe it would load faster after doing a restart), but not sure the back up worked.  Either way, once I was through loading the pictures, they were all there and visible and could be worked on.  I closed the application and allowed the suggested back up which was successful (to somewhere).  I restarted the computer the next day and voila, "No photos in selected folder", but the folder has the correct number of photos shown next to it, 1754.  I tried some of the suggestions, but nothing different so far.  If I go to that folder in Explorer, there they are, actually there are twice the number I pulled from the cards, but only did it once.  Not sure where to go from here.