Make sure your HDMI cable and HDMI inputs are working, you can check by connecting the HDMI cable with another external device to confirm if there is sound.

If the HDMI cable and inputs are working and there is still no sound from your cable box:

1. Power off both your TV and your cable TV box.

2. Unplug the power connections, wait 60 seconds.

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

In some cases, the problem can be caused by the HDMI compatibility setting with your cable TV box.  To change this:

1. Go to Settings > Antenna and inputs on your TV.

2. Choose the > HDMI > HDMI compatibility input your cable TV box is connected to.

3. Select HDMI 1.4. 

Note:  After adjusting the compatibility setting, you may need to select a different input and reselect the connected HDMI input for the settings to take effect