iMessage shows offline on iMac. Ok on iPad and iPhone. What do I do?

[iMore Question]

iMessage shows offline on iMac. Ok on iPad and iPhone.

Keep asking for password but doesn't take.

 

[Ledsteplin]

iMessage shows offline on iMac. Ok on iPad and iPhone.

Welcome to iMore! Try clicking the iMessage icon, go the messages menu at the top of the screen, preferences/accounts you should be able to log back in there.
Someone else may have a better idea.