Here's a video of the debug codes shown on the motherboard, slowed down 4x: https://1drv.ms/v/s!Am8wplmEWQV_ldJTiLxtqzECqfotmQ

CPU is a Core i7-6700K, turbo disabled and multiplier set to 40 (4.0GHz if I recall?).

RAM is 4x Corsair Ballistix at 2400MHz. I've tried removing all but one stick, tried each individually.

System started not booting yesterday, will not boot with all peripherals disconnected. Disconnected PCI-express GPU, two M.2 SSDs, hard disks, fan and front panel audio connectors.