RIG doesn't boot with 6 GPU

Hello,

PSU: EVGA 1300W
GPU: 4x RX480 8GB MSI + 2x RX480 8GB SAPHIRE NITRO+
RAM: 8GB DDR3
MB: ASROCK H81 PRO BTC
SSD: 120GB KINGSTON
OS: WIN10


I tested each GPU separately, and everything was ok.
Now, when i connect the 6 GPU at the same time, rig doesn't boot - yesterday it did but took about 15 minutes. Why?
All fans start running after startup but it doesn't boot, nothing shows up in monitor.
Tried connecting the monitor to different GPU and MOBO vga, nothing at all, doesn't boot.


I'm using hdmi to vga adapter, does it matter?

Thank you guys