While there may be a number of causes of no power, the usual one is that the bottom right screw that holds on the back circuit board has come out and has shorted out a section of the circuit. Usually it blows the 'P' fuse on the front board, but depending upon were the screw ends up it could blow the flash and drive boards or damage a section of the rear main board.

Also check to make sure you do not have bent CF pins - if the center power pins are bent and touch other pins they might blow the circuit. Usually this blows the 'K' fuse under the lower right shield plate on the rear circuit.