Random Restarts

[Retne]

I've been having this issue for a while now. My system randomly restarts. I'll be playing a game/browsing the web/working in a word processor when boom my system shuts off. Then a beat later it starts back up again. I've tried loads of things so I'll list them out:
-I've turned off automatic restarts on failures
-I've checked the event logs and the only errors I get is when it boots back up and tells me it didn't shut down properly
-I've replaced the mobo
-I've replaced the video card
-I've replaced the PSU
-I've replaced all the SATA cables
-I've run memtest86+ for 12 hours straight with no errors
-I've upgraded from the stock CPU cooler to a CM 212+
-I've reinstalled windows

The only things I haven't tried swapping out are the case, HDDs, or the CPU itself. Here is the current system:

CPU: i5 2500K
MOBO: Asus P8Z68-V LE
PSU: Seasonic X750
Video Card: BFG GTS 250
HDDs: Maxtor DiamondMax 10 200GB, WD Caviar Black 2TB, and a Hitachi Deskstar T7k500 400GB
DVD: Samsung SATA 22x DVDRW
Sound: E-MU 0404 USB Audio Interface
OS: Windows 7 Home Premium
CASE: CM HAF 922

Anyone have any ideas? I'm completely out of them. This has been plaguing me since I bought the 2500K on black friday.

EDIT: Well I've managed to find a way to force the random restart. All I have to do is run prime95 it seems. I don't think it's a CPU temp issue since the highest my temps went was 51C and it was lower than that when it restarted. I'm not quite sure what to make of this though.

 

[Dangman]

There is a possibility that it could be the CPU being defective.

Try running OCCT and Intel Burn Tool and see if you get the same results as Prime 95.