I have built my first rig using Nividia 1060 GPU's. SMOS Ubuntu USB stick.
So far I've installed 3 GPU's but when I boot it only shows the first one as green and the other two are red. The fan comes on for the first GPU but not the the other two. PSU is working and I'm powering the GPU's and risers from a 1200W corsair.
It is mining on one GPU right now. I've tried to adopt everything I have read on this thread and updated the BIOS. The BIOS has also been updated to the latest from Asus.
Any ideas why it only recognizes and powers one GPU?
Check your cables. Sounds like either the usb cable isn't running from the PCIe slot to the riser, the riser isn't powered, or the card isn't powered. Also, make sure you're starting from group 1 of the PCIe slots. My first B250 wouldn't boot if I didn't have the 4pin molex plugged in for each group even if I had the risers powered separately - so check the instructions on that, but you might have to plug it in as well.