Xbox 360 Problem

So, I modded my Xbox. I bought MW3, PES2012, Skyrim and AC: Revelations. All of them were cracked or well piarted games. PES and AC work perfectly, but the others don't. Skyrim and MW3 just give me a 'Play Game' sign on the Dashboard (i. e. game is not recognized), and I can't access Game Details. I select Play Game and after 3-5 seconds of the screen being black, the xbox goes back to the dashboard. What the fuck? What do I do?