iPhone 5s will not turn on? Changed everything outside componen level.

I have an iphone that has not been near water but has been dropped how hard i do not know. the screen was cracked so i replaced it for a good working one one week later the phone turns off and wont turn on i replaced the battery charging port power button and even the camera but no luck i tested the old and new parts they all worked the battery gives off good volts and so does the charging port. when i try to turn on the phone with an power supply at 3.7 nothing happens and like i said the screen works i tested it before and after and it has image. do i have to replace the IC chip........