My iMessage for my Macbook Air is not working. It says no delivered with a red ! next to it. I have tried serval different options on trying to get it to work to include logging out of iCloud and checking my date and time. I have done about everythin

My iMessage for my Macbook Air is not working. I have updated everything. My system is running on OS X Yosemite Version 10.10. When I go to send a message, it says no delivered with a ⚠ next to it. I have tried serval different options on trying to get it to work to include logging out of iCloud and checking my date and time and updating FlashPlayer. I have done about everything I can think of. Any help would be greatly appreciate!