Check to be certain that you don't have the mute function activated - it can either be assigned to a physical switch (the one that's beneath the volume control on the side of the iPad) or a soft switch that's in the multi-task bar. You can get to the soft switch by double-tapping the Home button, then 'flicking' the multi-task bar to the right to reveal some additional 'soft' controls. One of these could be the mute switch function.
You can swap the mute function between the hard and soft switches in the iPad's 'Settings' menu.
Tim