The only other thing I would like to add to this excellent answer from Phillip is the following. there is a possibility that your firmware does not recognize your new screen"s. Your iPhone NEED's to turn it off completely before you work on it. If your phone turns on prior to restoring it, there is the possibility that the screen will not be recognized, and only the backlight turns on, hence the white screen. I would totally remove the logic board for a couple of days and let it absolutely discharge. Once you have done that, disconnect the #4 cable and tilt the motherboard up so it does not touch the battery. Then connect all the cables for the front display etc. Place the logic board down on the battery, connect the #4 cable and shut down your phone correctly if not already done so. Once you have that accomplished, restart your iPhone in DFU and do a restore of the firmware. Hope I did not forget a step, let us know if it will work for you.