Calibre Not Detecting Kindle PPW

I have the second gen Kindle Paperwhite. However, for some reason Calibre isn't seeing it.

I'm running Windows 10 64bit. Caibre Ver 3.9 64bit.

Windows detects the Kindle and I can access it via File Explorer.

One thing that is different. I have Calibre's library set up on Dropbox so I can use the same library and be up to date on my desktop and laptop computers. Calibre sees it a c:\users\myname\dropbox\calibre

Thanks