Q: Computer crashing about 20sec into booting (even in BIOS). CPU or Motherboard? EDIT: we seem to have narrowed the problem to CPU or Motherboard. Is there any way I can identify the cause between these 2 without a spare part to test?
I was playing Minecraft for the first time on my 4 year-old rig and I think it might have killed my CPU (well, it was probably almost dead already..). Whatever the reason and how it happened, here are the symptoms.

*

*Computer crashed while playing. Had to restard it with power button.

*Didn't go through post. Restarted again.

*Went through post, OS selection screen, to Windows welcome screen, then crashed (nothing responds, screen freezes). Restarted again.

*I went in the BIOS to reset settings to default (no overclock anyways...), it crashed while I was scrolling in BIOS.

My computer has a history on the CPU level.. Only 6 months after I built it, it wouldn't boot up anymore. I narrowed down the problem to RAM slots 3 and 4. I RMA'd the Mobo, came back the same. The problem is probably the memory controller, which is located on the CPU (i7-2600k). I never RMA'd the CPU since I could run single channel using my 2x 8gb ripjaws in slots 1 and 2. That was a mistake...
The computer has been running fine for 3 years, no crash. Here is what I tried so far for this problem.

*

*CLEAR CMOS button, no change.

*Tried different sets of memory (Corsair Vengeance 4GB) in all different working slots, same error.

*Reseated the CPU, same error.
(checked for bent pins, took pictures, but nothing there. All the pins are straight and good looking)

*Disconnected all usb devices, same error.

*Removed the graphics cards and used integrated graphics, same error.

*Checked the CMOS battery, 3.24V output, it's fine. Same error again.

*Tried different OS (running Linux Mint) - though I doubted it would work because of BIOS freeze - didn't work.

*Cleaned every component (dust-off).

*Checked temperatures in BIOS before the crash. CPU is sitting at 43Celsius, normal. Voltages also look good in there (something like 12.3V / 5.1V / 3.2V (rounded, can't remember the actual values)).
*10. Tested SSD boot drive on another computer as secondary drive, it works. Since the bug happens even in BIOS, it's not in the boot sequence on the drive and the drive works --> I think we can rule this one out.

*Tried another Power Supply, still the same bug.*

Oh and I forgot to mention, my motherboard is ASRock so it has a Dr. Debug screen and it goes through every check and passes it before the computer freezes. When it does, there is nothing written on Dr. Debug screen.
Soooo. I think my CPU is dead. Does anyone have another idea or opinion? I don't have a spare working  Motherboard or CPU for testing... I would just like to identify what part I need to replace.
Here is my config, if it can help. Note that this is a 4 year old setup. Nothing was overclocked (the CPU was at 3.8GHz for a while, but I lowered it because it was useless.

MoBo: ASRock Extreme4 Gen3
PSU: FSP AURUM SERIES AU-700
RAM: G.Skill Ripjaws X 2x8Gb. 2133MHz, 9-11-11-31-2N. F3-2133C9D-16GXH
CPU: Intel i7-2600k
(unplugged atm) Graphics Card #1: SAPHIRRE Radeon 6950 2Gb with Arctic
Accelero Xtreme PLUS (flashed as a 6970)
(unplugged atm) Graphics Card #2: MSI Radeon 6950 2Gb Twin Frozr III
SSD1: Kingston HyperX SH103S3/240G SSD Drive
HDD2: Seagate Barracuda 2Tb
HDD3 and HDD4 (raid 1 array): 2x Seagate 5Tb(external drives took out
of enclosure, don't know the model)
No CD or DVD drive, i use bootable usb when needed.

Any help, comment, idea or opinion would be appreciated!!
Thanks
edit: edited the steps to add "checked bent pins"
edit2: added steps, added some temporary bold and italic on edits

A: Turns out it was the CPU.
Found a cheap G530 that I bought for testing and will resell (35$ CAD = 25USD).
I bet it was my fault, didn't change the thermal paste in 4 years and I used a cheap one in the beginning, -- thinking I would change it after max 2 years.
I found a cheap used Sandy Bridge i5-2500k that I'll use until next Intel's tick after Skylake about 2½ years from now. I don't really need that much power and don't feel like I need an upgrade right now.
Thanks for your help!

A: You may want to check the power supply. Voltages can read OK but as the machine boots it starts to draw more current and that can cause the system to just crash. If it is a no name brand 3 years is about right for a dying power supply. Replace it if there is any doubt before it fries the system. Most people overlook the importance of a good power supply such a Enermax, Silverstone etc. Look at Johhny Guru for PSU recomendations
