Using iPad, lost keyboard clicks

Have you got notifications muted ? Only notifications (including games) get muted, so the iPod 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

Try to Reset your device (and check volume settings?):

Press and hold both the Sleep/Wake button and the Home button for at least ten seconds, until the Apple logo appears (ignore the Slide to Power Off option that shows up first).