Can't transfer library book to my nook Glowlight

I've transferred many library e-books, but it's been a while.  I've downloaded the e-book to Digital Editions.  It used to be a simple 'drag' of the file to the device. My e-book is listed as a title in my library.  My nook isn't showing as a device on the L-hand side...there's no device showing at all.  Why is ADE not recognizing my nook?  Thanks.