Is there some trick to getting these Pico PSUs to power on the motherboard that I'm just not seeing? I have plugged the Pico PSU into the 24 pin connector on the mobo. Plugged the EPS pigtail into the CPU EPS connector on the mobo. Then plugged the 6 pin cable and barrel adapters together and plugged that into my server PSU's breakout board. I get a blue light on the Pico PSU so it appears to be getting power properly... but when I hit the power button on my rig, nothing happens. If I unplug the barrel adapter and plug it back in, I see the CPU fan spin for a second. This is the same behavior you will see if you are using a regular ATX PSU and you pull and re-plug the power cable on it. So it seems like everything should be connected properly... but it just won't power on. If I remove the Pico PSU, and plug in a spare ATX PSU to the same 24 pin/EPS connectors, everything powers up just fine. So, I know there is nothing else configured incorrectly. My server PSU powers my GPUS just fine, so I know the server PSU and breakout board works fine.
i had a similar problem, but this was because of my impatience, i was still trying to power my main gpu, the one on the pcie16x (usb riser part ) from a different psu and it didn't like that at all. and was causing the same symptoms you have now.
Thanks for the suggestion, but I've tried running nothing but the mobo with the Pico PSU that is directly connected to the server PSU and breakout adapter. I've connected no GPUs or risers to the server PSU and the Pico PSU still will not allow me to turn on the mobo.