So...the replacement TV worked for 2 months and then went black? When you turn on the TV, you don't see the manufacturer's splash screen? Power light on the TV? What happens went you navigate the TV settings with the TV remote?
You could connect another HDMI device to the TV to test, such as a streamer or Blu-ray player or, even though you probably don't have an antenna connected, you could test for just static. Press the HDMI Input button on the Contour remote to check for any life.
You could also try to launch an app installed on the Smart TV or update its software. It may be the cable-box.