My iPad has no sound when playing apps

System sounds have been muted.

System sounds can be muted and controlled two different ways. The screen lock rotation can be controlled in the same manner as well.

Settings>General>Use Side Switch to: Mute System sounds. If this option is selected, the switch on the side of the iPad above the volume rocker will mute system sounds.

If you choose Lock Screen Rotation, then the switch locks the screen. If the screen is locked, you will see a lock icon in the upper right corner next to the battery indicator gauge.

If you have the side switch set to lock screen rotation then the system sound control is in the task bar. Double tap the home button and in the task bar at the bottom, swipe all the way to the right. The speaker icon is all the way to the left. Tap on it and system sounds will return.

If you have the side switch set to mute system sounds, then the screen lock rotation can be accessed via the task bar in the same manner as described above.

This support article from Apple explains how the side switch works.

http://support.apple.com/kb/HT4085

This is how I have my settings for the screen lock and system sounds.

You aren't doing it correctly. Try it this way. Tap the home button to go to your home screen.

Go to Settings>General>Use Side Switch to>Lock Rotation. Then try the side switch and see if you can lock the screen. While holding the iPad in portrait mode with the button on the right - move the button down until you can see the orange dot by the switch. Did that lock the screen orientation? If the screen is locked you will see the padlock icon in the upper right corner of the screen. If that locked the screen, move the switch the other way to unlock the screen.

Now double tap the home button and swipe to the right to get to the software switch all the way to the left. Do you see a speaker icon there? Does the icon have a line through it? If it does, then system sounds are muted. Tap the icon to unmute the sound. Then tap the screen above the task bar to return to the home screen.

Try any app now and see if you have sound - or keyboard clicks.