If it's happening on a very regular basis, listen to your computer. Most newer computers the fans will speed up if it's getting too hot. If you hear that just before shutdown, you will have your answer. If you had one of the motherboards that yelled at you when it gets too hot, you would have your answer right there. It is a very annoying sound.
Good advice is to clean the dust from cabinet vents and look to make sure ALL fans are running.
Without looking it up, I think the video the OP mentioned is onboard, thus the GPU shutting down is most likely not the case. If tho, there is, a GPU installed, a failing Power Supply could also be the problem. Unless custom built, it's possible the power supply is borderline supplying enough power at all times for the GPU Be willing to bet PS he has is probably around 250W, 350W tops.
If you do not feel comfortable with getting into your computer to clean, DON'T. Take it someplace or have a friend that knows do it for you.