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

 

[Barty1884]

Are you monitoring temperatures of your GPU also? Could be that it's overheating and "crashing" as far as a display-out goes, without actually cutting power to your system overall.

Idle temps seem quite high for your CPU (assuming stock speeds)? Are you monitoring the temps under load? Touching the CPU and 'feeling' <40'C isn't really a solid enough test.

 

[nylealliss]

yes I'm monitoring them using MSI afterburner on idle my first CPU core is between 35-40C while I'm playing league its fluctuating over large ranges from about 45-55C. Had it turn off 2 times today, played 2 games then it switches off 5 mins after I finish the second game when I'm on the desktop with just league client and Skype on, then 30 mins later the same thing I after switching it back on it crashes within 5 mins with only league client and skype open. GPU temp is generally lower than CPU at about 40C.

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.