The issue here can be one of several issues, the following may apply:
- The HDMI graphics card may support HDMI Video, but may not support HDMI Audio
- You may need to set the HDMI audio device as the default sound device
- You may need to update your HDMI video card drivers for your version of Windows
- If your HDMI video card does not support audio, you may need to connect additional audio cables between the PC and TV