First, make sure your HDMI cable is working. You can check by connecting the HDMI cable to a different TV or monitor.

If the HDMI cable is working, and there is still no sound or you are having video issues with your HDMI device:

1. Power off both your TV and your HDMI device.

2. Unplug the power connections, wait 60 seconds.

3. Re-plug both devices back into the power outlet. 

If that doesn’t work, try changing the HDMI compatibility mode for this input:

1. Go to Settings > Antenna and inputs

2. Go to HDMI input > HDMI compatibility for the input your device is connected to.

3. Select HDMI 1.4

Note: the HDMI compatibility mode setting is only applicable to TVs which support HDMI 2.0 or higher. Check your TV hardware specs to confirm which inputs support HDMI 2.0 or higher.

If you are using an external speaker connected to the S/PDIF (optical audio) output or the HDMI-ARC/eARC input on your TV, and you are having audio issues, try changing the Digital audio output setting to PCM:

1. Go to Settings > Picture and sound > Audio settings > Digital audio output

2. Select PCM