Question Computer flashes LED's and Fan's briefly after pressing power button

[Nostradevus]

ISSUE:
When I press the power button on the PC the internal LED's and fans become active briefly (<1s). This build is 4 years old and has run with no issues until now.

PC BUILD:
PS - Corsair RM750i
MB - ASUS Z170-PRO
PRC - Intel i7 6700k 4GHZ Quad
Corsair H80i v2 liquid cooling
I do not list RAM or Graphics card as both have been removed from the system and the issue persists.

SOLUTIONS ATTEMPTED:
Removed Power to LED strip
Removed RAM
Removed Graphics Card
Removed HDD
Reset CMOS - Took out CMOS battery removed power from the computer, pressed power button a few times left sitting for 2-3 hours. Replaced battery, then power, then attempted boot
Connected another PS to MB (both MB and CPU connections)
All solutions were followed by an attempt to boot with the same issue persisting.

At this point, I believe it's probably the motherboard, but I wanted to see if anyone had any other ideas before specing out a replacement motherboard and processor. Thanks for any responses.

 

[rgd1101]

you can't boot without ram

 

[Nostradevus]

I knew that it wouldn't boot fully without RAM, but I figured it everything would at least stay powered up (might have been wrong about that, but its only one wasted test). I only removed RAM once for testing and it was present during all subsequent tests. The only items I left out after their individual tests were the graphics card and led strip.