Question PC freezing frequently

Mar 16, 2019
Heyas, looking for a lil advice.
My PC keeps freezing, almost always during video playback.
The first error in the image happened while I was watching youtube. The video froze, audio continued for 5-10seconds, then froze and the PC rebooted by itself shortly after. When I logged back in my second display was moving of its own accord. Primary display is hdmi, secondary is using DVI.
The second error happened as I was writing this post as I tried to alt-tab to take a screenshot of cpu-z & event manager.
This is driving me insane as I need to watch lectures and study on this thing.
Sometimes I can play games for hours (WoW, AC Odyssey on ultra or v. high settings) without a hiccup.
Just froze again as I was installing cpu-z.
It is a fresh install (<1 week ago) of genuine win10 home on a brand new samsung 1tb nvme m.2 ssd. It was happening on the old samsung sata ssd aswell.
All drivers windows updates are up to date. All temperatures are at 30-40degrees after a freeze/reset.
*Froze a third time as I decided to use speccy instead of cpu-z... all in the space of minutes.
*Edit: After trying to isolate the issue for ages, and finding no faults with individual components, I thought it might be the PSU. I am using a cheap thermaltake case/psu combo. 500w, but not 80+ rated or anything. I have just ordered a 650w 80+ gold psu, both to eliminate that as a potential problem, and to future proof for a new system.