I have 2 Rx480 and 1 Rx470

Working perfect with one card directly plugged into pcie x16 and 2 usb powered risers

Now I bought another Rx480 with usb riser

So my problem is with 4 cards plugged into Mother board PC (Win 10) does not boot...
Fans are spinning on all 4 cards
Anybody know why??

Maybe its because of PSU?
Its 750 Watt