OK I know this could be annoying, but we have to start with the simple things, instead of asking you 1 by 1, I'll just ask you all at once.
1) Is the 8 Pin CPU cord plugged into the socket at the top left of the motherboard, same goes with all of the other connections. Also make sure that they are fully plugged in.
2) Is the RAM fully seated in the slots, I ask this because that was what was wrong with my build and was a really simple fix.
3) Make sure that the MB standoffs are not installed where they are not being used as they could cause a short in the motherboard.
4) Do you have any way of testing the power supply as it could be defective?