Try the following steps to resolve audio issues with your Smart TV:

1. Check that the TV is set to the correct input selection
2. Verify that the cables connecting the sound system to the TV are properly connected
3. Verify that the external sound system is receiving power
4. Make sure the external sound system has been set as the sound output device in the settings of your Smart TV
5. Make sure that the volume settings of the external sound system are not muted or set too low