As Samet said if it says sign in failed you should get a log message. This should tell you whether it is a incorrect password or whether the user does not exist in the system. The user you are trying to login with may have been locked out of the system so check whether the boolean blocked on the account is not ticked. You should try to login first with mxadmin and the default password that you have set. If you could provide some more information as to your issue i will be able to help you further.