Rig won't post after installing 4th card

[felix920506]

Building a new mining rig
Specs below:
Amd athlon 3000G
Team DDR4 8GBx1
Asrock B450 Gaming K4
WD Green 120gb m.2 sata ssd
radeon rx580 8gb *4
evga 850w GA power supply

all works fine with 1~3 cards
when I plug in 4th card it doesn't post

[nbminer]

Have you enabled Above 4G Decoding in bios?

[felix920506]

I can't find that option on this board
bios version is P3.90

[miner29]

Are you plugging all 4 directly in the mobo...if you are try using risers for some / all of the gpus.  When plugging directly into the pcie bus...it requires the mobo provide power through the pcie slots.  Riser remove this power draw from the pcie bus. 

[nbminer]

I can't find that option on this board
bios version is P3.90

It should be in the Boot Screen options