I know this is an older post but I ran into this just recently.
I was having trouble with a Asus Maximus VIII Formula not posting outside of the case. On board LEDs would light and cycle but the CPU cooler would not spin and the MB would not post. Come to find out it wasn't grounded enough to turn on. Installing the PSU and the MB in the case let the MB post.
Just thought that adding a step with a continuity check with a multimeter on the MB screw holes or installing it in the case could help other people.
Engineerd got a reaction from Ben17 in README: How to respond to a no POST or no power up situation
