iPhone 4 not turning on at all

hi,

i having my repairing shop but i dont know about this problem please help me

i had an iphone but it want turn on it was working fine just turn off nothing happen with it. after that i check bettry its good working it other mobile i dont know about power switching points where they coming from i check through meter on iphones board it seems no power it power jeck can any body tell me where are the power points or any other solution