Q: iMessage will not deliver messages on my MacBook Pro

I have made sure all the send&receive options are synced up between my iPhone, iPad, and MacBook Pro. I have entered all the activation codes for text message forwarding, and still my MacBook pro iMessage is not delivering messages. It also is not receiving any of the messages I have gotten on my iPhone or iPad. It is signed in and connected, however when I try to send one it comes up with the red exclamation point and not delivered. My iMessage used to work perfectly fine before the update to Yosemite. Any suggestions or solutions would be greatly appreciated.