1. Ensure that your HDMI cable is plugged firmly into the HDMI ports on your Smart TV and HDMI device.

2. Check that your TV's HDMI port is the same number or version as your HDMI device.

3. Test the HDMI ports on your Smart TV by connecting a known working HDMI device. If your device still won’t work, consider replacing it.

4. Reset the TV. Turn your Smart TV off from the power cord, wait for a few minutes, and then turn it back on. This can sometimes resolve connection issues.

5. Check your settings. Some Smart TVs allow you to adjust the HDMI settings from within the options menu. Make sure your settings are correct.