GMod causes my PC to reboot under certain circumstances

Hi. I’m doing some 4K screenshots (by the help of DSR) since months, what you can see on my deviantART account. But since some days, when I set to 4K and go underwater, my PC is taking a crap and resets (tested in gm_abstraction_extended). It also happened while I played The Sims 3 (before I put a FPS limiter in) and when I play Miitomo on BlueStacks for a long time.

Here’s some of my specs:
AMD FX™-8320 Eight-Core Processor - 3.50 GHz
8 GB RAM
Windows 7 Home Premium (64 bit)
1 TB HDD
NVIDIA GeForce GTX 970 - 4 GB
1680x1050 native resolution (I don’t have a better monitor right now)
PSU unit: Corsair VS550
Motherboard: ASUSTeK COMPUTER INC. - M5A97 R2.0

I got the computer on the start of this year from my deceased brother. He bought this computer on Mifcom.de on the start of 2016. It was probaly never used for a year until I got it, so it may be dusty. I also played The Sims 3 alot on the computer since months and I limited the FPS of that game to 30 just some days ago. I heard that The Sims 3 rapes graphics cards. And on my GMod, there are over 900 addons (yes, call me crazy) and notice some graphical glitches when I use my Physgun: https://steamcommunity.com/sharedfiles/filedetails/?id=1111535717

Can somebody help me? Is one of the things I mentioned above the reason for the sudden restarts?

Going to need some additional PC stats from you…
mobo model, PSU model, etc.

[editline]20th September 2017[/editline]

I ask because a friend of mine’s computer acts similarly if he pushes too hard. We thought it was the PSU, it wasn’t. Our current theory is his mobo is not rated for the power the cpu/gpu/smoothie machine was drawing. He didn’t have this issue until he started trying to run everything on ultra after getting a new gpu.

could be your machine is overheating too, had a similar issue way back and it was because my pc was overheating itself.

My PC wasn’t that loud. It was under 55 °C. When I play Planet Coaster, my PC’s loud as hell and even reaches almost 60 °C. Haven’t played it since months. (still waiting for guest creator and pools)

Like I said above, maybe Sims 3 damaged my video card. Other people reported that, too. I played Sims 3 alot on this PC and first, after several months, it restarted while I’m playing Sims 3 and right after this, capped it’s FPS to 30 and it runs fine. But it may be too late.

PSU unit: Corsair VS550
Motherboard: ASUSTeK COMPUTER INC. - M5A97 R2.0

Sorry if I can’t really get all the stats, it’s almost a decade since I had a tower PC unit. Or I’m just too dumb…