there is a simple solution to this one! when repairing a phone in which the screen is destroyed,
1st) open the phone as if the screen were off and you were preparing to take off the lcd/screen
2nd) rather than taking off the screen, first remove the battery connector from the logic board.
as long as there is no power getting to the lcd, the screen repair can be done. Also, sometimes if the battery percentage is low before the repair and you have to unplug the battery, it will take a while (i've had upwards of 45minutes) to turn back on once the repair is complete.