X399 Taichi

Ok... admitting doing dumb things is not fun... but this might help you. Be careful when plugging into this socket. it is oriented differently from the 8 pin socket, but yet I was still able to somehow successfully plug the 4 pin connector into the socket facing the wrong direction. For some reason my system wouldn't boot! Go figure! Once I realized what I did, it booted just fine. For some reason, even though it shouldn't have been possible to plug it in the wrong way, it surprisingly plugged in wrong easily... so check if something as simple as that is the issue. 

lancec19, I do not understand where you are plugging in the connector.  The power supply should have a 24-pin, 8-pin and 4-pin for the CPU.  All should be plugged into the CPU connectors.  The video cards have their own set of power connectors which should be plugged into the video cards.  There is also a video power connector on the board.  Some connectors may be 4+4 pin or 4+6 pin.  The CPU power connectors should be labeled CPU and the Video power connectors should be marked PCIe.  Do not connect either into the other's socket.  Failure to power up seems to be associated with connecting the PCIe connector into the CPU receptacle or vice-versa.  Please let us hear what you find.  Enjoy, John.