The Dropbox icon is gray in my menu bar and the desktop app won't start.

Thanks for the fast reply.  And I'll also add that this is the second Mac computer on which this has happened.  My assistant, at another location, was having the problem the other day.  She would add something to the dropbox in the Finder and it wouldn't update to Dropbox on the web.  I tried everything on hers and finally gave up.  Now about a week or more later, the same thing happened to me.  I tried reinstalling the application (though I don't know that I was able to properly uninstall the application aside from dragging the application to the trash--there are probably other files I don't know about hiding in the system folders?) and I tried give Dropbox permission and access via my system settings, clearing caches, checking the network, there is no firewall.  I recently upgraded to the latest Mac operating system.  I wasn't kidding about wanting to upgrade, probably after the first of the year, but I'd want things to be working before I do.  I hope you can help.  I was going to try to figure out how to uninstall properly as my next course of action and then try reinstalling the dropbox application.    

The image is a still but that blue diamond is a frozen frame of the animation that just keeps going forever and ever.  If I hover over the little gear settings icon, it will say "connecting" but it never seems to connect.  I suspect it has to do with the upgrade, though my assistant hasn't done it yet.  Could have been the update prior.  I may not have noticed that it was happening to me.  I rarely use the menu bar icon.  Thanks once again.