You would see the error in the log that says:
Wowza Streaming Engine Manager could not connect to the Wowza Streaming Engine service (http://localhost:8087). Verify that the Wowza Streaming Engine service has started and is running.
As far as why, here are some suggestions for you in this article:
There are several forum posts on this as well if you enter port 8087 in the search bar above. Here is a post that may help you as well and offers several suggestions:
Lastly, see this image from the following article:
