Computer dies every time I join a Counterstrike map - weirder than a BSOD

I have a R9 280X GPU and an ASRock Z97 Extreme4 motherboard, and 8GB (2x4GB) of HyperX Fury RAM. I'm running Windows 10.

For the last week, I haven't been able to join a Counterstrike game without my PC dying and being unusable for a good few hours after. It doesn't exactly BSOD, instead it just freezes up and the screen does this.

When I reboot, the motherboard shows a 'b2' error on the LED display. I found this advice on Tom's Hardware and tried it, but pulling the CMOS battery and reseating the RAM have not fixed the issue. In fact, just pulling the CMOS battery doesn't even work unless the whole system is unpowered for hours. If I just unplug, pull the battery for 30 seconds, reset it and reboot, I still can't get into the BIOS. I can only get into the BIOS after a few hours of being unplugged. I've also installed the latest GPU drivers but to no avail.

My current theories include:

• Motherboard is broken
• GPU is broken
• One RAM DIMM is broken

But I'm not really clued up enough to know which it is for sure so I can replace it. It's also worth noting that it only happens in Counterstrike (I don't play any other games, so it's possible it's just anytime the GPU/RAM are under strain). Should I stress test RAM/GPU to diagnose it? Is one a likely candidate?