PC shutting down and restarting without warning

Dec 6, 2018
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Hi all, i have had quite a large problem with my pc ever since i had it. this is my first one so i am relatively new to the details of the problems and solutions. the issue is that my computer shuts its self down without any error or warning at all and then re-boots its self automatically a few seconds later. this usually happens when playing high demanding games and my recently bought VR oculus rift headset. I am able to get at most an hour of play time on some games and on others a maximum of 10 minutes before the computer shuts down and re-boots. i have visited a lot of forums and have found no one with a similar issue and a solution.
I have completely ruled out the possibility of there being any overheating as when playing the games i've monitored each hardware piece and all are well within the temp limit. similarly i have tested to see if the games are taking up too much processing power and everything is below even 50% on all components. I have also ruled out any software errors or viruses as ive completely deleted and reinstalled windows and my files in hope that it would fix the issue.
i have owned this pc for just over 1 year and bought it all as one so i assume all the components should run smoothly with each other.
My specs are here:

CPU - Intel core i7-4790 quad core
16 GB RAM
64-bit windows 10
GPU - GTX 1060 6GB
motherboard - ASRock H81M-HDS R2.0
PSU - says, 100 - 240 VAC

Have tried countless times to solve this problem but not getting anywhere, would really appreciate some advice or help. thank you