Interesting I havent had that kinda of GFX hang in awhile. At least not sense my X800xt. It sounds like the GFX card itself is shutting down, and causing the whole OS to hang. It can still be overheating tho, very good chance. Back when I had alot of issues with this, I set up my GFX fan to 100%, back then i had to use ATItool, but I'm pretty sure the newer drivers let ya do that now. Another concern, which i really hope it isn't it, would be a power issue. Its common for the OS to freeze in this manner if there is a sudden loss of power to any random component due to a PSU not being able to provide power during a full load situation. I wonder what kind of PSU it has in that comp. I'd expect a reputable company such as alienware to insure the PSU they put in a comp can easily meet the demands of the rest of the computer, under full load..