Black screen when i try and load game.

I am using the latest version of multiman, and i have backed up world at war on to my internal HD, I have left an original game in the console ( GTA ) .
So when i goto multiman and click on world at war it takes me back to my main dash board and now i can't see GTA but now i see world at war so i click to play and all i get is a black screen .
Could someone please tell me werer i may have gone wrong!.

Thanks Nic