[SOLVED] CPU and PSU fans turn on an off 3 times than on but I get no POST

[elibrussels]

Hello,

I am facing painfully confusing issue with a PC build and I can't seem to find a solution.

The behavior I am seeing is:
Powering on the system makes the PSU and CPU fan spin for about a second, they stop. Looks like the system goes off. It than goes on again and stops again.
On third start the fans spins in a stable manner but I have no POST.

Tests i've done:
1- replaced the CPU with a tested working CPU
2- tested the CPU in another system, that system booted with no issues (in other words, same issue with 2 working CPU's)
3- replaced the RAM and tried all the 4 slots on the system in dual channel and with just one barret
4- tested with another PSU that I know works
5- removed all peripherals (GPU, case fans, ssd, hdd)
6- replaced the motherboard
7- removed CMOS battery with the PSU unpluged and turn on without the CMOS battery. Put back the battery and turned on as well. Same result.

I basically replaced the entire hardware yet I am faced with the same issue and as a result I have many more white hairs.

Any ideas of what can cause this?
In my thinking, if it was a short I would not have a stable fan spin on the 3rd loop. This makes me think I am dealing with some safety mechanism?
P.S - no hardware warning lights turn on on the MB.

The build:
CPU; i7-6700 (also tested wth Celeron G3900)
MB: Asrock h370m pro 4
RAM: corsair vengance lpx ddr4 2133mhz
PSU cooler master g550m (tested with two of these)

 

[Phillip Corcoran]

That motherboard doesn't support Celeron G3900 or i7-6700. Hence no POST.

See support list Here

 

[elibrussels]

Embarrassing oversight... thank you!