System won't boot for unknown reason. Help!

[andyblanchfield]

My desktop shutdown last Saturday morning unexpectedly and I am unable to get it to work at all. It was working fine for most of the morning then suddenly and unexpectedly shut off.

The motherboard lights up [the RGBs] but no fans start up and nothing else happens. Here are the specs and what I've tried so far:
MB: ASRock Z270 Extreme4
CPU: Intel i7 7700K
RAM: 2x8GB Vengeance LPX DDR4 2800Mhz
GPU: EVGA GeForce GTX1080
PSU: EVGA 850GQ
HD: Samsung M.2 960 EVO 1TB
CPU cooler: Corsair H100i V2
Case: Corsair 400C
-- I've replaced the MB with another new one of the same. I've replaced the older one PSU [EVGA NEX750G] with the newer one.
-- I took apart everything. Cleaned the interior of any dust and rewired everything.
-- Removed the CPU cooler, cleaned it and the CPU and repasted and reseated.
-- Removed RAM and reseated.
-- Tried booting with just SSD, RAM [one at a time and different slots, all configurations possible] using onboard video
-*- Basically took it all apart and started as if was a new build-*-
Doesn't even make it to post. Nothing. Zero. Zilch happens.
Nothing but the MB lights [which now do not come on either as of 10 minutes ago] come on. I am at a loss here. Any suggestions would be great.
[I went through the troubleshooting guide I found here and tried or verified all of those as well.]
I have no spare - RAM, CPU, GPU, MB, cases etc. to swap out anything.

 

[npiet1]

Remove the 4/8pin does it power?

 

[andyblanchfield]

Remove the 4/8pin does it power?

No. No combination of anything I've tried has resulted in anything closer than what I wrote in the OP. A millimeter of travel by the rear case fan before stopping and the LEDs on the MB light and glow and that's it. No other lights or sounds at all.

 

[shknawe]

sounds like cpu died.

 

[andyblanchfield]

sounds like cpu died.

I'm tending to lean that way as well. Thank you for taking the time to respond. I appreciate it.