Try tapping on your id in Settings > Store and logging out of your account on it and then log back in and see if that makes any difference.
If it doesn't then a second thing to try is closing the App Store app via the taskbar and see if it works properly when you re-open the app : from the home screen (i.e. not with the App Store 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 the App Store app to close it, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.
A third option is soft-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.