Pc shutting down after few mins

[Sparsh Bhatli]

UPDATE: It was my motherboard it was faulty.. I replaced PSU and ram but it was still happening I changed my motherboard it worked...

As the title says my pc shutting down automatically after few mins of usage sometimes most of the times it turn on and just shuts off... its 2years old and It was happening once a week for about a year so I didnt thought it was a problem. it didnt give any error or anything just suddenly turn the cpu off. Any suggestion whats wrong with my pc. I dont think its overheating got 3 fans top side and back and clean whole cpu once a month.
My specs
Processor- i7-4790
Ram - 8Gb
Motherboard -ASRock H97
Hard drive-2Tb (replaced 10 days ago bcoz run out of space)
Graphic Card -AMD Redeon R9 270x Dual-X
power supply- Corsair VS550
I was using UPS Numeric 600EX
I tried removing graphic card but it still didnt turns on sometime and turn back off when it does turn on.Tried using it without ups(directly plug in socket)
should I get a new power supply or it is UPS fault ?
I dont know whats going could it be motherboard fault ? any help please?

EDIT : I am 100% sure its not overheating
http://i.imgur.com/keOiTVa.jpg

http://i.imgur.com/zgJSPCJ.jpg

 

[slyverine]

top suspects:
Temps: if you don't check with a software like speccyy, you can't be sure.
PSU:Maybe it;s faulty if you can, try another one.
Power Button: Maybe it stacks and initiates shutdown.
Motherboard: Nothing specific here, it might be faulty.

 

[Sparsh Bhatli]

I am 100% sure its not overheating
http://i.imgur.com/keOiTVa.jpg

PSU is not cheap here I wanna know more before I go and purchase any parts

Power button is good no msg of shutting down... it completely shut down quickly like someone remove the power cable

I dont think its motherboard too but idk maybe it is.
anyways thank you for your answer really appreciate it.