Messages on MacBook Pro not working I can't get Messages to work on my Macbook Pro (retina).  One day it just went offline, and I can't get it back online.  When I try to login I get this screen and it won't accept the password, even though I input the correct password. Can anyone help get it back online?  I've tried all the suggestions listed here so far without luck :-(
Do you have 2-factor authentication set in your Gmail account? Sometimes, this seems t lose the password for a device with symptoms like yours. 

If that's the case, a solution is to go to your Gmail account settings (at Google, not on your MBP), revoke the password for the MBP and create a new one