so you get as far as the faceplate?
the leds still come on when you put the cage, LCD, and home bar on with the screws?
i have had this happen to me a few times with the phats. make sure that the wires are not being pinched by the cage. I would do what was suggested above and place electrical tape on the part of the cage that is touching the wires. sometimes the wire will get pinched and the covering opens up a bit which leads to shorts.
after checking the wires, connect the brace, lcd and home buttons. insert battery and turn on. see if it works. if it does, try to either gently press on each side cage to determine where the short is happening. it will give you an idea on where to look further