It seems like your Mac isn't recognizing your TV via the HDMI connection. I'll be happy to provide some information on this. The following articles have some information that may help in a situation like this:
Frequently asked questions about using HDMI with Mac computers
What do I do if my Mac doesn't recognize my HDTV using the HDMI connection?
Try these steps:
- Leave your Mac turned on while you power off the HDTV.
- Unplug the HDMI cable from the Mac and plug it in again.
- Power on the HDTV.
macOS Sierra: Use your TV as a display
Get help with video issues on external displays connected to your Mac - see the section title ' Blank or unusable display '
Have a good one!