Sound in games not working on my ipad3

Have you got notifications muted ? Only notifications (including games) get muted, so the Music and Videos apps, and headphones, still get sound.

Depending on what you've got Settings > General > Use Side Switch To set to (mute or rotation lock), then you can mute notifications by the switch on the right hand side of the iPad, or via the taskbar : double-click the home button; slide from the left; and it's the icon far left; press home again to exit the taskbar. The function that isn't on the side switch is set via the taskbar instead : http://support.apple.com/kb/HT4085

If you've set Settings > General > Use Side Switch To to control rotation lock, then to set mute/unmute you need to double-press the home button to open the taskbar at the bottom of the screen, then swipe that bar to the right and the icon at the far left should then be for 'notification mute'. There are instructions and some screenshots in that link.

Double-click the home button i.e. the button just below the screen.