Unfortunetly it seems that someone for whatever reason has Locked your account. This is very simple to do using easy account lockers. Your account could be locked for 12hrs-24hrs-permanent.
Here is a solution for unlocking your account:
To do this you must first sign into a edit server or msg server for a new cookie. To do this navigate your browser to click here , click here , or click here .Once you are here you must sign in with the account that is locked. Once signed in just exit out and sign into messeger.
If this does not resolve the situation you may have to create another user ID.
I hope this isn't the case, maybe someone else here will have some other options for you to follow, as they are very compuer savvy here:)