Mail asking to add new account when opened

Hello. I am using a MACBook Pro with Yosemite. When I opened Mail this morning it asked me to add a new account and is not showing my current email accounts under the inbox. I hot canceled as I don;t want to add a new account and the mail program shut down. So I shut down my computer and restarted and the same thing happened. So I tried opening Mail again and went to re-add an exiting email account. Mail told me the account was a duplicate so I canceled and Mail shut down again. How can I get around this problem? Thanks.