Hello @redcrest0517. Which HDMI input were the GoPro set to this time? Also, do you recall any change on the video resolution used? Were you trying to view the same video, or new videos? Try using a different port on the TV, if available, and make sure to set the connection to the correct Input.
By the way, a new firmware for the HERO7 Black was released yesterday. Be sure to update your camera. Firmware download is available at https://gopro.com/en/ph/update/hero7-black .