Why cant I play games on my hackintosh??

[zamdam]

I installed iAtkos 5i and managed to get everything work, including my HD 4870 video card.

My question is, why am I able to play a demo I downloaded from apples website, but I cant play cod4 that I downloaded from a website. Once it mounted the .dmg it verified the disk...

But when I go to play it, the screen turns black and then about 5 - 10 seconds later, Im guessing the computer freezes cause my keyboard doesnt do anything when I press caps lock, it has a light on it when i press it to let me know its enabled. Also, my monitors power button starts flashing instead of staying on..?

Thanks in advance.