take out your other hardware, network card, sound card, drives etc.
Its probably that one of these is faulty and causing the crashing. You've replaced the RAM, PSU and mobo so that pretty much rules out the primary culprits.
HAve you tried stress testing the CPU with something like Prime95?
I take it you've checked that the CPU is running at a good temperature?
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"