When attempting to send a test email, we click Send Test but then nothing happens. We should be seeing a pop-up like the one below:
While sending a test or final message previously, we checked the box in the pop up window that says "Prevent this page from creating additional dialogs."
Our site is now preventing those boxes from showing, and thus stops us from sending out messages.
This can be resolved by resetting our browser. The following guide shows how to reset Chrome, Firefox, and Internet Explorer. http://www.howtogeek.com/171924/how-to-reset-your-web-browser-to-its-default-settings/