[Sgat8516]

Well, there's more than 1 reason, for the game software, to reject your system from being able to operate some games.
Some, in fact, will not run at all, without certain things.
Most common (and even expierenced myself, numerous times), was, newer games that required T+L (transform and lighting support), or P+S (pixel + shader). From what I understand, only Nvida+Radeon graphics chips (certain versions, mostly newer ones I'm assuming), are capable of running those graphics. I'm sure someone could give you a much more technical reason why 99% of the games that actually require this feature, won't play games, but...
If the game will not run, its not going to run. There's a reason the game won't allow you to play, and its because the manufacturer decided NOT to provide supportable options, for those running non-supported chipsets.

(personally, bought a top of line Dell, plenty of ram, nice proc speed, clearly blew all but 1 thing out of water, in requirements, but, couldn't run certain games, without -downgrading- to a graphics card, with a Radeon Chipset...)

(this is why I download+test -ALL- games before buying, because, I can't return the game after opening, and if I can't play, its no use)