Oddly enough I have the same issue, but its more at the 1-3 hour mark of running the game. It only happens while running FF14. I thought it was a CPU overheat issue, and checking the heat with CPU Fan showed it well within tolerance. I replaced the heatsink with a massive Cooler Master unit, adding two nice fans inside. The heat dropped much lower, but I'm still having the problem intermittently. I was running two 6950s for graphics cards, and now I'm down to one, but that didn't solve the problem. The Corsair HX 750W power supply doesn't seem to be faulty, as I've already went over it with a multimeter.

The weird thing is that this only happens with FF14. I can't go over three hours without a complete shut down. I did four hours on The Secret World at max settings last night, no problems. I have no problems with any other game for long periods of time. The heat readings were higher than when running FF14. Its the weirdest thing, because I've been building PCs for about 15 years now and I'm a programmer. I can't seem to find any errors and I'm not catching any BSOD.

CPU: AMD X6 1100T
Grafic: MSI 6950 (down to one, with no improvement - and I've tried both of them individually)
Power Subly: Corsair HX750w
RAM: 16GB Corsair
Mainboard: MSI 890FXA-GD65
My OS is on a Crucial SS Drive and I run everything else on a secondary WD drive, both of which have been checked numerous times. I had FF14 on the SS Drive with the OS at first, which was awesome, but one of the crashes formatted my SS drive for me!