Mail Password Help

Before when i used ail, i would launch it and it would log into the account automatically, but recently, its been asking me for my user name and password. so i put in the information and clicked the checkbox "remember in my keychain" but when i logged in again it still asks me for my password. so i went into mail preferences and the box with my password was empty. so i entered it and saved and relaunched. but it still asked me for the password. and the password box in preferences was empty again. i tried deleting the account and making it again but it still wont remember my password. any ideas on how to fix this?

please help