Make sure you updated the firmware image, follow the instructions in theis thread: http://avic411.com/index.php?/topic/27807-fx31-complete-firmware-image/page-1
Read the instructions and follow the steps in the first post.
I never seen a unit not turn on, at the very least it should take you to the pioneer screen. If it won't turn on it is a hardware issue. Maybe you should check your 12 V power and ground wires? Did you do anything besides what was instructed in the service menu?