Boot device LED flashes then boot loop

[satocar]

Hi,
I got stuck on POST a couple of days ago, and after I cleared the CMOS (removing the battery and shorting the CLRTC) it starts up and goes through the component LED cycle until it reaches the BOOT_DEVICE_LED, which turns on with the ASUS logo on the screen, and the whole system stops (LED flickers off) and loops again. I've checked RAM by taking out one and throwing it in every slot, but memOK! causes the system to instantly shut down. I unplugged all the cables except fan power, and tried using system graphics. Obviously, the boot drive and HDD are unplugged. Can't really think of anything else to do... should I try it with some other RAM, or could it be some other component?

ASUS Z170-A
Vengeance LPX DDR4 8GBx2
6700K
ASUS STRIX 1070
Corsair H80i
Corsair CX750

Thanks in advance. All components are <1y old.

 

[satocar]

Turns out disconnecting all of the externals plugged into the mobo seemed to be the problem. A USB3.0 hub I accidentally plugged into a USB2.0 port may have caused some sort of power problem. I guess I gotta remember to disconnect everything inside and outside for diagnostics.
Thanks anyway though.