PC keeps turning off

[nylealliss]

Having an on going problem with my pc, It keeps turning off. This has been happening for about 6 months now. At first it was very rare maybe once a month, now it is happening very often sometimes 4 times a day when i'm using it a lot. At first i thought it was an over heating problem as my CPU does run fairly warm idle ~35-40C. However, i cleaned out my PC and reapplied thermal past to CPU. this was to no avail, recently it can happen at any time even if i'm just watching YouTube videos, or playing low intensive games like league of legends. It happened again earlier today, while i had been on desktop for 10 mins after playing a game of league, so i opened my case removed my CPU heat sink and felt my CPU and it didn't feel like it could have been any warmer than 40C. Another reason why i don't believe temp is the problem is that once after taking the heat sink off i forgot to plug the fan back in and my CPU temp went to 90C before i realized and plugged it back in and there was no crash.
Sometimes after switching off when i switch it back on its starts for a second then goes off leaving only the power button and lights on my GPU on, this is normally resolved by switching off at the plug for 10 secs and then back on again. Any help would be much appreciated, i suspect its an issue with the power supply or mobo.

Any ideas what else could be the problem, here are my specs:

Intel Core i7 i7-4790K CPU (Quad Core 4GHz, Socket H3 LGA-1150)

EVGA Nvidia GeForce GTX 980 Superclocked Graphics Card (4GB, GDDR5, PCI Express 3.0)

Gigabyte Z97MX-Gaming 5 Intel LGA1150 Z97 express chipset (4x DDR3, 4x USB3.0, 4x USB2.0, HDMI, DVI-D, DSUB)

HyperX FURY Series 16 GB (2 x 8 GB) DDR3 1866 MHz CL10 DIMM Memory Module Kit - Red

Silverstone SST-ST85F-GS - Strider Gold Series - 850 Watt (SST-ST85F-GS)

WD 1TB SATA lll Desktop SATA Drive - Blue

Running windows 10

Samsung 850 EVO 2 TB 2.5 inch Solid State Drive - Black



Here are some screen shots of temps on League:
https://imgur.com/a/63Wra

i added some more screen shots to the album, they are from ESO and Mount and Blade. After taking the last screen shot I exited the game and came to upload the images and about 2 mins after closing down Mount and Blade it switched off again. Also got some idle temps for about 10 mins.

 

[Mark RM]

It's almost always (more than 50%) the power supply and that's what we basically test first if temperatures are OK. Even the best PSU in the world can fail.

 

[nylealliss]

It's almost always (more than 50%) the power supply and that's what we basically test first if temperatures are OK. Even the best PSU in the world can fail.

I've noticed that when i play games it happens more often. If i play more intensive games like TW: Warhammer 2 or PUBG, it turns off guaranteed within 30 mins. Whnen i play less intensive games like League its generally fine in game if it crashes its during the load in screen or within the first 15 seconds or when the game ends and the nexus blows up. Are these likely to be due to power supply?

 

[Mark RM]

Generally when you game and are placing the largest load on your system is when it stresses the PSU the most.

The issue is that when it's NOT the PSU, it's going to be CPU power delivery circuitry on the motherboard... usually the caps get bad and crappy when you experience stuff like this. But mostly it's the PSU.... that's where I'd start.

 

[nylealliss]

Generally when you game and are placing the largest load on your system is when it stresses the PSU the most.

The issue is that when it's NOT the PSU, it's going to be CPU power delivery circuitry on the motherboard... usually the caps get bad and crappy when you experience stuff like this. But mostly it's the PSU.... that's where I'd start.

That's where I'll start then. Thanks for the help.