I recently built a new PC, which has been running fine up until a BIOS update yesterday.
I normally wouldn't update BIOS unless there were issues and in this particular case, the AMD FX-6100 CPU I'd ordered wouldn't run CS:GO without a BIOS update... made the update, game works perfectly, all is well.
Now, randomly, the computer will just completely turn off. No 'proper' shut-down, no BSOD, just an instant power-off. It does appear to be entirely random, not when the computer is doing anything demanding or otherwise.
It's relatively frequent, it's rare that the PC can be used for longer than 30 mins without it doing this.
The BIOS is the only thing that's changed since it started happening. I've tried updating the BIOS with progressively older versions with the same result. After the computer turns off, the only way to turn it back on is to turn off the PC at the PSU switch for 5-10 seconds, turn it back on then start up as usual.
Temperatures are all normal, so it's not like the CPU is overheating and shutting down - as I said, the machine doesn't necessarily have to be doing anything demanding, could just be sat at the desktop.
Windows event viewer just shows a critical 'Kernel-Power' issue, as you'd expect but doesn't give anything else away.