it goes back to home screen when I turn on a game?

i bought an iPod touch 4th generation from the shop CEX, a second hand shop. i have one game called geometry dash which works fine and doesn't need internet but then i downloaded a game called clash of lords 2 which does need internet and whenever i tried turning it on it would start downloading and then go back to the home screen and i tried everything to try and make it work. for example turning the hole thing on and off again, but it wouldn't so i got a new game which is called clash of clans and that also needs internet but it has been working for the last 3 weeks until today when it suddenly did the same thing clash of lords 2 did. and i don't know what to do.