Lightroom 6 will not Export

I'm done editing my photo and when I'm ready to export, I take the appropriate measures.  Highlight the photo's I want to export from the Library, File> Export> Select Settings> click Export... and then nothing happens.  The export window goes away as if I hit cancel (which I didn't).  I've tried multiple ways of exporting, i.e. with preset, from previous, right click the thumbnail, click export shortcut button on bottom left of screen... Nothing seems to work.  It used to work.  I changed nothing and have no plug ins installed.  I've found nothing identical in the forums...