Windows 10: Why does my PC keep restarting with BSOD or just plain turns off?

Recently my PC has been either randomly restarting, randomly turning completely off with only the power light on, or randomly turning off, rebooting and then not displaying anything. Every so often there is also a visual static that flashes for a fraction of a second

:)

 

Random Restarts, No BSOD

He mentioned that he had done that above. Also I provided a BSOD details app. There were no BSODs to report.

 

Random Restarts, No BSOD

Reboot and hit F8 to get into the Windows Diagnostic Settings before Windows boots. Turn off "Automatic Restart on System Failure." This way we can completely rule out BSODs. Sometimes a PC will BSOD but the PC will restart so quickly that the BSOD is not even rendered.

 

PC reboots (no BSOD) on CPU stress

Hi fellow TPU members,

not too long ago, the box my gf's PC was transported in gave way on the stairs. Yes, you got it right, that sent a PC tumbling down a flight of steps alright.

Stuff broke. Also, stuff remained intact somehow.

I bought her a new case, new CPU cooler and we removed the floppy drive, so far so good. But the PC started crashing for no apparent reason, without a BSOD.

I tested:

• Memtest86+, left overnight, 0 errors
• Scanned the HDD for errors, nothing there
• Left FurMark burning up the GFX card and drawing some power, no problems there
• Ran Ubuntu from a Live CD doing nothing special, didn't crash
• Ran OCCT, Linpack, Prime95, all 3 caused reboots within minutes
• Oh, and I disabled "Restart on error" so I'm sure it's not a BSOD.

Now, I can still try and test something CPU intensive on Ubuntu, but my guess is the CPU didn't survive.
Before I do anything drastic like whippin' out the magic wallet and get her a new AMD quad, is there anything I didn't see?
I'm guessing the motherboard could be borkered as well, but can I check that other than replacing the CPU with a working one?
Any suggestions on which proggies I can use from an Ubuntu Live CD to stress the CPU?