Possible explanations for an android device being unable to produce sound are that there is a downloaded application preventing sound from playing or that the speakers themselves have been damaged. It is also possible that a headset or other plugged in device is not working.
To troubleshoot an Android device, you should first make sure that there is nothing plugged into the device that would be playing the sound. If the problem persists, check the programs installed on the device and the current settings to make sure they are not preventing the device from playing sound. If the product is still not making sounds, a factory reset can be performed to reset the phone to its factory settings. If the problem persists further, it is likely a problem with the hardware that will likely need repairing.