If you're using the inbuilt speakers check the volume buttons on the front of the screen are functioning, when pressed you should see a volume bar displayed on the screen. If nothing appears try using the volume buttons on the remote to test if that's the issue. 

If there is a soundbar connected to the panel ensure it is powered on ( should see a light on the front of the soundbar), the cables are connected to the input of the soundbar. Check the sound settings of the panel by opening the inputs icon on the home screen. 

Select the icon in the bottom right corner.

In the top heading use the small arrows to scroll across to 'sound mode'. Ensure sound output is selected to 'external device'.

If you're connecting a laptop with HDMI ensure that the volume is turned up and that the output device is set to the CommBox Panel instead of the internal laptop speakers. 

For Windows: in the bottom right corner right-click on the speaker icon in the System tray and select 'Sound Settings'.

At the top of the Sound settings page, you will see an option to select your output device. Select the little drop-down arrow and select your CommBox.

For Mac computers click the apple symbol in the top left corner. Select System preferences, sound, output and select HDMI audio.