Suddenly I can't log in to iMessage on my computer when my password is correct?
It was working just fine till it logged me out all of a sudden. Isn't log in my iCloud apple ID and password? I don't understand.
MacBook Pro
Is it just loading for a while and then stops? If so, resetting the PRAM resolved that for me.
See how here: OS X Yosemite: Reset your computer’s PRAM