Broken ipone 4, no home button ribbon

i just got a iphone 4 (att) off of a buddy of mine, needs a digitizer (he said it still works but is faded bc he pinched a wire) and also is missing the home button and the ribbon to for it so its missing the whole home button assembly. but the phone is all put together in one piece, but the phone will not turn on but it did before he took the home button out...

so my question is, is it true that a missing home button assemly will cause the phone not to power on??