computer shuts down instantly

[JuicedSage]

hello i have sort of a problem i cant figure out my pc shuts down without warning and my first thought was its my psu and i changed it still having the same problem anybody know what it is here are the specs and yes its not that amazing gaming rig its just for watching linus tech tips and stuff

gt 710 2 gb ddr5

msi 2A9C (its oem so even if i want to overclock cant do it)

intel i3-550

12 gb ram 4x2 2x2

and now the psu's i tested fractal design 750 w (its overkill i know)

a antec 350 w

corsair VS550

 and all of them got it after like 3 hours its really annoying anybody know whats up?

[TempestCatto]

Can you check your temps? Does it only happen under load or even when idling?

[JuicedSage]

my temps all normal and idling loading just random

[Xtenchen]

ive had this same problem earlyer this year still havent found a fix, i brang my rig to 3 pc repair stores they couldnt find the problem eather, but now mine fixxed and doesnt shut down, i hated this problem because i had no clue what it was, im pretty sure this has something to do with GPU becuase ive relplaced everything except that becuase they are overpriced back then.