PC freezes for ~20sec & restarts, noticed while browsing firefox

It happens randomly. It happened more when I browsed the web with Firefox, and now it happened the 1st time on Chrome too...
Already checked the RAM with MemTest for DOS overnight (OK)
Stress tested the GPU for 5 minutes at 100C with no artifacts (OK)
Had few bad blocks on my Seagate HDD but fixed it with the Seagate tools for dos (OK !? )
Tested the CPU with Prime95 (OK)
Everything inside the case is clean of dust and all cards have been re-seated after contacts cleaning.
I also formated and re-installed windows 7 and updated all the drivers.

Here is the error details according to WhoCrashed:

This was probably caused by the following module: ntoskrnl.exe (nt+0x4ADE0C)
Bugcheck code: 0x124 (0x0, 0xFFFFFA8004BFA038, 0x0, 0x0)
Error: WHEA_UNCORRECTABLE_ERROR
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This bug check indicates that a fatal hardware error has occurred. This bug check uses the error data that is provided by the Windows Hardware Error Architecture (WHEA).
This is likely to be caused by a hardware problem problem. This problem might be caused by a thermal issue.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver that cannot be identified at this time.

I'm also uploading the required ZIP file.
Any thoughts??

Cheetah

Your Product key is from an OEM Asus while your Motherboard is a Retail version. You would need purchase a legit version of Windows .

Are you an MSDN subscriber ? Those keys aren't for sale .

You used an OEM key which doesn't come with MSDN subscription . slicha

Bsod 124 is hardware related. How log did you test your CPU using Prime ? Test your RAM as well using memtest86+

RAM - Test with Memtest86+