Thunderbird stopped downloading email. When it starts, all I see is the rotating circle at the top.

Thunderbird stopped downloading emails today. I'm using 38.5.1 on vista. I haven't changed anything - in fact, I downloaded another email client and was able to retrieve my email using the same server settings. I prefer Thunderbird however. When I open Thunderbird, the normal window opens and I can see my old email messages and filtered messages etc. However, I don't see the normal "server connection" messages in the lower left field. The only thing I see is the rotating circle. The "Get Messages" button also has no effect. If I click on any other folder,, it opens and I can see the messages. Clicking on the Inbox just gets me the rotating circle. I am able to send messages. It seems that only the inbox is affected. Thanks for any input!