Diagnosis
The monitor's speakers require an audio signal via the 3.5mm audio-in port. They do not receive audio through the HDMI or DisplayPort video cables alone on this model.
How to Fix It
You need a separate audio cable. Connect a 3.5mm audio cable from your PC's 'Line Out' or 'Headphone' jack to the monitor's 'Audio In' port. Then, press the monitor's menu button, navigate to 'Audio', and ensure 'Volume' is not set to 0. Also, confirm Windows sound output is set to your PC's realtek or motherboard audio, not the HDMI audio device.
If That Didn't Work
Test the 3.5mm cable with headphones to confirm it carries sound. If the cable is good, check the monitor's audio settings: ensure 'Mute' is off and no other audio processing is enabled in the OSD.
Heads Up
The internal speakers are low-power, 2-watt units. They are suitable for system sounds only, not for media playback or gaming where volume and bass are expected.