Before I start with my problem, I'd like to give my PC's specs:
CPU: AMD FX-8350 (not overclocked)
CPU Cooler: Hyper 212 EVO
GPU: MSI Twin Frozr V GTX 970 (not overclocked)
RAM: 8gb DDR3
Mobo: MSI 970 Gaming
PSU: XFX TS-550w
Storage: 240gb Sandisk SSD; 1tb Western Digital HDD
Case: Corsair Carbide Series 200R w/ stock fans, no added fans
OS: Windows 10
Also, I built this computer in late 2015, so it is about 2 and a half years old. None of the components have been replaced since then, and the newest addition is my CPU cooler, installed last year because the stock cooler was really loud and still had my PC running hot. Anyway, on to my issue...
This started happening about a week ago while I was trying to install a game from Steam (Dark Souls 3). I started the install late at night, and left it installing while I went to sleep as it is a pretty large game. When I woke up in the morning, my PC's power button was flashing like it does when put in "Sleep" mode, but I noticed that all the fans were still running and my GPU lights were on. I tried pressing keys on my keyboard and shaking my mouse and got no response. I pressed the power button and nothing happened, then I held the power button for a while and still nothing happened. I tried pressing the "hard restart" button next to the power button and still nothing happened. I then just unplugged the computer from my surge protector, then waited a few minutes and plugged it back in. Everything seemed to go back to normal: there was a normal boot, Windows didn't say anything went wrong when it started up, and I even checked the event logs from the previous night and nothing suspicious had occurred.
I dismissed the problem and started playing the game, and, after about 40 minutes, my screen went black, the power button flashed, and my computer became unresponsive again. At this point, I thought that the problem might have something to do with the game since any issue like this had never happened before until I installed the game, so I looked up several possible solutions to minimize PC crashes while playing the game. While I believe these solutions made the amount of time I was able to play before a crash longer, the crashes still persisted. Again, I just thought that they had to do with the game, until one night a few days ago, I was done with my computer and was going to shut it off like I do every night, when the screen went to black and it crashed like before, with the power button flashing and fans and such still running. Keep in mind that the game was not running and hadn't been for a while at this point. It was then that I thought this was probably a hardware issue.
At first, I believed it was my GPU failing, so I updated the drivers and things seemed normal for a while, but the crashes still happened after a while of PC use. Most of the crashes occur after playing Dark Souls 3 for a while, but there have been 3 crashes where no game was running, 1 of those in which no programs (except background ones) were running at all. Whenever these crashes occur, the only thing that can get my PC working again is unplugging it and replugging it.
I posted about this issue on another forum and got some advice from a user there. He said that it might be caused by the VRMs on my motherboard getting overheated and failing and suggested that I try reapplying thermal paste to my CPU cooler. I did that today but I still had a crash after a few hours of having the PC on and running a few games. This problem has become very frustrating over the past week as I can't seem to be able to simply watch videos on YouTube without my PC crashing like this after a while. At this point, I believe it might be a PSU or a motherboard issue (like the user on the other forum said), but I'm not 100% sure. Has anyone experienced anything like this or know someone who has? If so, any possible solutions are very much appreciated.
Any further information regarding my PC/hardware can be provided if needed.