My iMessage won't change from "offline"

I use iMessage all of the time on my Macbook Pro. However, in the past few days, I have been unable to use it. It won't send or receive messages because it says I am "offline", even though I am connected to the internet and have clicked "My Status: Online" MANY times.

I just updated everything completely, and I've only had the notebook for a few months. Anyone know how to fix this??