April 16th Update: This specific issue was resolved last week
However if you are still having sign-in problems please use these "life lines":
1. Read Messenger Help (In Messenger -> Help -> Help Topics)
2. Ask the Messenger Community for help
3. Ask Messenger Support for help
You maybe having problems signing in right now
We are working as fast as possible to get it fixed.
You can check out the service status here.
I know how much it sucks when you can’t sign into Messenger.
On behalf of the Messenger team – we are really sorry.