Have you checked the temps and such? Maybe use Afterburner and monitor the temps and the GPU activity. Benchmark the unit for stability issues if you can. Any error statements in the Event Viewer at the time of the crash? Hope this helps
Also an overheating cpu can crash the system (depending on BIOS settings) so grab HWMonitor and have that running and keep an eyeball on it while gaming.
Don't forget to run a memtest.