Recently my iPod started stopping playing games or allowing apps downloaded from the app store to work. On attempting to open an app or game, it would redirect you back to the home screen immediately.
Found the answer on the way to work today on the train, and thought I'd share it here, as I managed to fix it by tethering my iPod to my Android phone and connecting it to the internet via my portable Wifi hotspot created on my phone.
All you have to do is simply sign back into the app store. I did this via updating an existing app I had on the phone. Downloading a new app would have worked as well.
See here for more information...