PC won't boot with more than 3 GPU's

[avxkim]

Hi, here's my GPU miner config:

Windows 10
PSU Thermaltake Gold rated 1475W
MB Asus Z270-P (set all PCI-E to Gen2 and enabled 4G)
8GB Kingston HyperX
Core i3 (LGA1151)
SSD Kingston 128 gb Sata
6xGigabyte GTX 1070
6xUSB risers x1-x16

My rig starts without any issues with 3GPU's. If i use more than 3 GPU's it won't boot, just hangs on the black screen and blinking cursor. Later i've enabled 4G thingy, then it started to boot after 5 minutes, then in Device manager it detects it, but drivers won't install (windows one). If i add 5th GPU it won't boot again. What could be an issue?

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[deztroyr1]

Hello,

Did you update your BIOS to the newest version?

[avxkim]

Yes, i did through EZFlash to the latest bios. What could be else?

[savs]

set 4G enabled ?

[fanta21]

I have the same mobo with 6x RX 570 and Windows 10. My rig wouldnt boot until I installed Windows in GPT mode instead of MBR.