Covers Suddenly Stopped Showing Up

[Kevin In CT]

Hi all, I've had an problem with the covers if my books not showing up in the library. All I see is something like a B&W title page with no covers for each book. It used to work fine but sometime back, this behavior began. I'm using an old Samsung Nook tablet with the Calibre and I've tried just about all I can find including doing an ebup toe pub conversion or doing an ePub to mobi conversion with no luck. Any and all help would be appreciated, thanks!!