Help please PC crashes during gaming

[PoisonMako]

when i play intense games my computer just turns off i have a 

ASUS GTX670-DC2 2GB

AMD FX-8350
Gigabyte 990FX UD-3 AM3+ 
G-Skill Sniper 16GB  at 1600 4 dimms
XFX 850 Watt 80+ Bronze PSU
1 64GB SSD for boot 
2 HDD one 500GB for Steam one 250GB storage
Corsair H80
Windows Home Premium 64Bit

im sure its not the GPU as i put my older GTX 460 in and ran into the same problem where when the GPU stays at around 65C the whole computer turns off anything really below 60C it stays on
my mobo got sent back from a  RMA where it wouldn't post tryed the cards in both PCI Express slots as well same result
BOTH sets of 2x4GB dimms of ram are brand new
maybe PSU? didn't want to spend another 100+$ on a new one since i was hoping to either get a second 670 or a newer card soon
CPU is also brand new (as new as like 6 months gets... updated from 1100T)
some of the items are not new but still well within 2 years old...
don't think its the H80 seeing as its keeps my CPU at a nice 30C and at 50-60C during gaming

please help as much as you can or want i was hoping to be able to play games as i wanted and was hoping to get into some more but have been unable or unwilling with this problem

[Bluejay0]

Have you overclocked the CPU?

[Godlygamer23]

How much heat is coming out of the power supply?

[Glenwing]

Run some memory diagnostics too.

[JoshM]

May sound like a stupid question but did you delete all old drivers when you were swapping cards?

[PoisonMako]

CPU is not overclocked  and all drivers are all up to date and where deleted and replaced when swapped and i have no idea what the Psu temp is

[FTW_Perverse]

What do you mean the computer just "turns off"?  You mean the screen goes black?  Or the computer actually shuts off (no power)?

[PoisonMako]

it turns off as in no power no nothing just off