Main thing I would look at is the voltage for your 12v+ (idle and under load). Is there a way you can get them from inside Windows (like Giga's mobo tool)? You can get the idle voltage from BIOS.
Your system can get all flaky if the 12v rail is out of range (i.e. +12.6 or -11.4). Ran into that problem myself quite recently...750W PSU, AMD CPU, 2GB RAM, x850XT, single 80GB HDD, no optical...thing had NOTHING in the box other than what was absolutely necessary for the system to run, and crashed every time I ran Warhammer. PSU was putting +12.75v over the 12v rail. Changed PSU to 350W El