Hello.
First off I should mention that I am an IT engineer.
However, all IT engineers run into issues they can't resolve themselves and sometimes have to seek help elsewhere! Here is mine.
So I have a custom built (by myself) gaming PC (AMD powered; CPU and GPU, specs/CPU-Z included) with liquid cooling on the CPU and the majority of my games run flawlessly on a 19% CPU overclock. (Which is stable...99% of the time) I reinstalled Mafia II on Steam and started playing today and all of my video settings are of course auto-set to the highest available settings in-game, including Apex PhysX on (the problem I believe may be related to Apex PhysX). In about roughly 20 minutes into the game (the first story mission) my system completely shut itself down. So I booted back up and on the boot POST it came up with "NB Overheating detected" or something along those lines. I am unsure as to how best to cool the NB as as of current it's temperature is at 64'C at the time of writing this thread. I am using HWinfo to check that temperature and of course it shows "T2 - 64'C".
Specs:
Motherboard: Asus Crosshair V Formula-Z AM3
CPU: AMD Phenom II X6 1090T 3.2GHz (stock) - 19% overclock - 3.8GHz
RAM: 14GB Corsair Vengeance DDR3 1333 (I think)
GPU: AMD Radeon R9 280X 3GB
Cooling: Corsair Hydro H90
PSU: Corsair AX1200i