You might need to close and reopen the app. If you double click the home button, the apps you have open will appear at the bottom. Press and hold on the AppStore one, then press the red close button. Then go back to your home screen and open it again
Whenever I have difficulties with my idevices I go to the support forums in the apple website. I do a search for the prob and can usually find an answer. If all else fails I do a post. There is always someone on there who can help me.