I have a series of photos on a flash drive, and they also appear on my MacBook, in Finder. I have tried to import them from each source and I got the files to be listed in Lightroom 6, but it shows 0 photos. I've tried to re-import them and when I select the source, the Import Dialog box does not light up. Can anyone tell me how to get these photos into Lightroom? Thanks.
You can't 'reimport' into a Lr catalog without first removing that file(s) from the catalog.
Try File | New Catalog, Import working left (source), top (method), right (destination).
The photos are already in Lightroom. DO NOT reimport them. Go to the Library Module, click on All Photographs, and find them there, and then you can perform any Lightroom task on them.