The Mysterious Desktop Computer Shut Off...

Computer shuts off randomly (after hours unplugged)
Scenario:

1. Computer shuts off on cold boot (after hours unplugged/switched off) at Windows desktop around 2 minutes.
2. After the shut off - powering on the PC again and it runs perfectly (passed all burn-in test). Runs pc games perfectly 8 hours to 12 hours. Ex. Wasteland 2

Troubleshooting I made:
1. Cleaned PC thoroughly using compressed air.
2. New thermal paste applied on the processor.
3. Video card and Memory contact cleaned with rubber eraser.
4. Reconnected all cables and checked for loose cables.
5. Bought a new power supply. (Deepcool DE530 400 watt rated)
6. Removed all hardware. Only the Processor and motherboard are running.
7. Memtest and MEmtest86 memory at boot up. Passed. No errors.
8. New CMOS battery
9. Bios jumper reset at motherboard.
10. New Windows 7 home installation. Dual boot removed. (Linux)
11. Capacitors not bloated. (top and bottom)
12. Bread-boarding (motherboard and Processor only) still shuts off at cold first boot.
13. CMOS downgraded to original version.
14. Checked power strip and Automatic Voltage Stabilizer/Regulator for fault.

After troubleshooting it still shuts off randomly at the first cold boot.

Processor: AMD Athlon X3 435
Motherboard: Asrock N68C-S-UCC motherboard.
DIMM: 2x 2gb DDR3 memory kit 1333mhz
ROM: Asus DVD rom RW
Nvdia GT630 DDR3
Old PSU: Great Wall Black series 450wl (old)
Brand New PSU bought to check if old PSU had a problem): Deepcool DE530 rated 400 watts
Reply to darth.gabby
2 answers Last reply
More about mysterious desktop computer shut
  1. Asrock N68-S-UCC does not DDR3 memory. You probably have ASRock N68C-S UCC. Not knowing your motherboard model often leads to flashing the BIOS version of a different model.

    It may also be you choice of memory. 2x 2gb DDR3 memory is a vague description that doesn't identify clock speed, and whether it is a kit of two or two random single modules.
    Reply to Calvin7
  2. Hi! It is an Asrock N68C-S UCC., just a typo.
    The memory modules are working fine together for years.
    Thanks.
    Reply to darth.gabby
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