If it's happening on all the apps that you've downloaded from the App Store, but not the Apple built-in ones, then try downloading any free app from the store (as that appears to reset something) and then re-try them - the free app can then be deleted.
Otherwise have you tried closing all apps completely and then seeing if they work when you re-open them ? From the home screen (i.e. not with any app 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of each app to close them, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.
If that doesn't work then you could try a reset : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.