Your PC seems to be overheating and, as it's designed to do, then switching itself off. (All electronic circuitry produces radio frequency emissions; it's possible that the switching device in your PC is transmitting on a frequency that interferes with the operation of your safety device).
So the first things to check are that your computer's vents aren't blocked and that the fan is running normally. (My friend had a computer that kept shutting itself down. When I went round to her house to take a look at it I immediately noticed that she'd got a bar towel on top of it, so that she could put her coffee mug up there. The towel was hanging down over the back of the computer, obstructing the vents. I simply removed the towel and the problem never occurred again!).