Is it my gpu or CPU rebooting my system?

So, when I play games it randomly reboots pc with no bsod. When I first built my PC it never had this problem. But recently it's been rebooting in games more frequently.
My CPU and gpu are both at cool temps. And everything is hooked up fine.
I tried memtest and no problems.
I tried occt CPU stress test and it lasted 15 mins before rebooting.
Tried furmark and it reboots after 10 seconds.
Occt PSU stress test also reboots pc after 5 seconds.
My asus bios settings on low power saving mode lasts longer than the other high power modes.
I'm thinking either PSU or GPU is bad..

What would you suggest?

I have:
Asus p8p67
i5 2500k
12gb ram
Gtx 570 card
750 watt PSU with:

+12v DC has 60A and 720W
-12v DC has 0.5A 6W
+5VSB has 3A 15W
+5VDC has 22A 150W
+3.3VDC has 22A 150W

(another note... No lag before any reboot, graphics on highest settings)
3 answers Last reply
More about rebooting system
  1. Usually this is a power issue. Do you have a second PSU for testing?
  2. Thanks for fast reply. I can borrow my friends one tomorrow. Hopefully it'll explain everything..

    The fact that my CPU stress test last longer than my GPU test means that GPUs require more power than CPUs?
  3. This is not a Power Issue because it either shut down OR burn your hardware... This is most likely to be Windows Issue or Virus... What kind of hardware cause a system to reboot if you haven't done anything to it(If you did, your system probably isn't stable)?
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