Why cant i access one of my email accounts, and how to fix?

I have a Iphone 5, and when for some reason one of my email accounts seems to be bugged. When I go into setting and click on it, it canels the setting menu and goes to my home screen. in the mail icon it asks for a password, I put it in and an imap error message pops up. i cant access only that email, to delete or make changes. what do i do?