Turn all your graphics down to low
I've had it happen mainly due to overheating on the graphics card
You'll get shut offs due to not enough power for your graphics, i.e. a graphics card will need 150 watts when your PSU can only push 100 more causing the overload protection to kick in. The only time overheating will affect it is if you are going above the TJMax which is usually above 100 degrees C for GPU's and around 90 for CPU's.
Also some motherboards will have overload protection similar to the PSU which will kick in if a certain component like the CPU or RAM is needing more than it can supply it.
What is clear for the OP is shutting off is definitely a hardware issue rather than buggy software, if it was software or driver issues he would of either got a BSOD or a normal crash.