Mail cannot connect

Urgent help needed! My Mail system is in trouble. When I try to log in to get or send mail, I get a message saying “Recovered Messages (Windows Live). Imported 1,600 of 16,000 messages.”
And that’s as far as it gets. Cannot view or send messages.
All suggestions welcome.
Model Name: iMac
Model Identifier: iMac16,2
Processor Name: Quad-Core Intel Core i5
Processor Speed: 3,1 GHz