Please list what you have tried, to help narrow down suggestions that may be tossed out.
That's a nice build for sure, now when it locks up, is it just the game that you can CRTL-ALT-DEL out of or do you have to push the reset button on the case? Have you updated your vid drivers? Have you applied most recent game patches? Are you running overclocked? Is there anything else that locks up the PC (i.e. watching movies, benchmarks, web browsing, etc).
I would say download memtest, furmark and prime95 and run each for a while, start with furmark in stability mode for VGA stress test, allow to run for 5-10minutes, then do memtest to ensure memory errors aren't causing the issue, then do prime95 in blend mode (or small fft's for cpu only, blend stresses cpu, mem and nb). Odds are if you're running stock none of these should be causing the issue, but it never hurts to see.
Any more info and details you can provide is much appreciated! And welcome to TPU! Hopefully we can getcha sorted and gaming in short time!
