Inbox completely deleted

This morning when I tried to log onto my email address, I kept getting an error message that said "This account does not have an Outlook Web App mailbox". I tried several different times and it would not let me view my inbox. Several hours later, I tried to log on again and it let me, but this time it had automatically done some kind of upgrade to Outlook that I had not made. Now, none of the different accounts I had connected to my main email address are connected and none of my emails from the past four years are available. Is there any way to bring back the thousands of emails that have now been deleted?