Hello there and welcome to the Wowza support forum.
What is the source of this stream? Is it an IP camera?
If so, try playing back the source in VLC. Is there black screen in source in VLC? What the audio and video info in VLC for the source? Look at Tools > Codec Info. And what do you see there for the Wowza output, is there video codec info?
You can also test the Wowza output in VLC. Is there a black screen with the Wowza output?