Check the following settings in the Prowise menu:
1. Port
2. Audio
3. Visual
4. Display
5. Settings
Is the volume set at a value higher than '0'?
Is there a physical connection with earphones on the Prowise ProLine? 
- If so, the audio is muted since it is playing through the earphones.
- In the settings/audio/output menu, select internal (only audio output via the touchscreen) or both (audio output through earphones and the touchscreen)
- Or remove the earphones (2) so the sound is no longer muted.
Check whether the output is set to External.
- If so, the speakers are muted because the sound is set to play though an external speaker.
- Select 'internal' or 'both' to activate the speakers on the Prowise Classic Line.
Check whether the Mute feature is activated.
- If so, the speakers will be muted.
- Disable the mute feature to let the sound play through the speakers of the Prowise Classic Line.
In case the internal PC module is used as source, check:
- The Windows volume settings
- Device that is playing (in the Window audio settings)
PC monitor 2 Intel Display Audio
- Audio drivers.
Update the Audio drivers for the PC monitor 2 Intel Display Audio device in the Windows device manager.
In case an external PC is used as source, check:
- The external cabling of the external PC to the Prowise Classic Line.
- Whether the Windows volume settings are correct.