No boot, except on random occasions. Potential dead Motherboard?

[Andre01100]

I have narrowed it down to either the CPU or Mobo. I was unable to independently test them so I cannot distinguish which it is. Right now I've got the PC disassembled. I'm heavily leaving towards it being the Mobo and would send it off for RMA except that it will occasionally work. The few times I've had it on it works at 100% completely fine.

Any advice on things to try or potential fixes? Ive tried reseting CMOS already.

Edit:
MSI Z170A Krait Gaming 3X
I7-6700k

 

[SgtScream]

Flip the switch on the power supply off, then hit the power button. Flip the psu switch back on and see if the computer boots.

 

[Andre01100]

Flip the switch on the power supply off, then hit the power button. Flip the psu switch back on and see if the computer boots.

Nope.

 

[SgtScream]

You've said you narrowed down the cause to be the cpu or the motherboard. How did you do this? If what you say is 100% true, 9 times out of 10, it's the motherboard.