Get Messages button quit working

Suddenly and without warning, Thunderbird is no longer able to get messages. It just says DONE. Trying to get messages even from the menu bar does nothing. It doesn't prompt me for anything. Composing and sending work fine! I know it's an old OS Win7, but my other Win7 machines work fine. I'm afraid to do an uninstall and reinstall and lose very important messages. Can someone please help? Thanks so much! Jack116.0