How Do I Fix An iPad With Sound That Isn't Working?
First, make sure you haven't accidentally muted the iPad. To check, try flipping the side switch (it's the one pictured below):
If your side switch is set to control orientation lock instead of muting, you will have to check the mute status using a different method. In iOS 7 and iOS 8, swipe up from the bottom of the screen to launch Control Center. If the top right icon looks like a bell/alarm, make sure it is deselected. In iOS 6 or earlier, double-tap the home button and then swipe to the right. Look for the bell/alarm icon and make sure it's deselected.
If it's still not working make sure your iPad is updated to the newest version. Go to Settings > General > Software Update to check if you are using the latest version. Update if possible. If that doesn't help, restart the iPad by holding down the sleep/wake (power) button and the home button until the Apple logo appears. Additionally, you could also try resetting the iPad by going to Settings > General > Reset > Reset All Settings.