Mobo: ASRock H81 PRO BTC R2.0 S1150 Intel H81
GPU's: 6x Sapphire RX570 Nitro+ 8GB

I never had any problems booting the system before as I was setting the rig up whilst the screen was always plugged in and now when everything is set up I must plug the monitor in to boot the system. Never ever had this kind of problem with any other computer systems.