I had this setup (asus p5kc, gigabyte 8800gt, corsair pc2-6400, e8400) for a while, no problems whatsoever. Once computer crashed during game, then I started to see artifacts during booting, nvidia driver didn't load and in device manager there was information that 8800gt doesn't work. So i thought my card has fried (it was factory overclocked version) so I bought 8800gtx.
Now the weird part..everything was ok for couple of weeks, games worked, no crashes, then i started to see artifacts again(during booting as well). Sometimes i can start system with video card working properly, sometimes not. Compter works fine until i start the game, then after a while it crashes hard. Should I start with changin PSU? Or maybe there is something wrong with MB?, Sisandra doesn't show anything unusual