BIOS current? , PCPartpicker claims RX 580's are compatible.
https://ca.pcpartpicker.com/products/video-card/?compatible_with=sktCmG#c=391
It is a pre 2012 BIOS , but it is the latest so that's not the issue. A lot of BIOS setups pre 2012 can't run newer generation cards, Could be the issue. Some H61 chipsets won't run them too.
Yes.Have you tried different out ports?