First, make sure that you check the following:
- Your monitor does support sound. PC monitors do not support sound, while TV almost always support sound.
- If you use an HDMI-to-DVI adapter or cable, then you cannot get sound. DVI does not allow audio signals to go though. You should be able to use the analog mini-jack to get audio.
- Make sure your TV is not muted, and volume is high.
- If you have a second HDMI cable, try replacing it. Some very cheap HDMI cables do not work properly.
If you are sure your monitor supports audio and it is not automatically detected, do the following to force audio to go through the HDMI cable:
- Go to "Monitors"
- Go to the details of the monitor with the issue
- Click on the tab "Advanced"
- Activate "overwrite raspberry configuration"
- In the "raspberry configuration file" field, enter the following line:
- Click the "Save" button. After a while, your Raspberry will reboot.
If the above does not work, try getting another HDMI cable.