Before you start worrying, make sure that the sound is not switched off and the volume is not turned down. You can do this with control buttons on the side of your iPad/iPhone.
If you're on your iPad and the side sound switch doesn't work, it might be set up to lock the screen rotation instead of muting the sound. To change this, go to Settings -> General and change the "Use Side Switch To:" option.
If you still can't hear a thing, try rebooting your device. Simply hold the sleep/wake button on top of your device until the screen goes darker. Then confirm by sliding the button right. Once the screen is completely black, you can turn it back on by holding the sleep/wake button for a couple of seconds.
In case you're still experiencing problems with the sound, please contact us using the contact form.