What a stupid idea - we know but please, please double-check that you have correctly typed in the username and password. 

If you are sure, most of the time the password is simply incorrect in this case please our "Forget my password" function.

As an additional idea: check in your mailbox if you have received any communication from us regarding your account if it has been restricted, inactivated or closed for Terms of Service violation or any other reason. 

If that is the case follow up with this information about what you need to do.