There can be many reasons for msn account not working. Few of them are :

1.Either user has entered incorrect login details. Check the user id and password and also that capslock is off.
2.If its a sign in issue then reset the password. Click on the link , "cannot access the account? "on the login page and then follow the instructions on the screen.
3.Try login with a different browser. Sometimes it can be a browser issue.
4.If user is not able to send or receive emails then try clear the history and caches.
5.Close every other application running in the system.
6.Disable the antivirus and try again. If still the problem is there then enable the antivirus again.
I7.f user finds that the account has been blocked then if logged in, immediately change the password and if not able to log in then reset the password. User may asked to fill up a form so as to identify the user to send the notification for password reset.

If still the problem persists, user can call at the msn customer service number and ask the executives about it. The service is 24/7 available to help and guide users.