iPhone 4 cracked and wont turn on

my boyfriend threw my iphone 4 on the ground out of anger and my screen was already cracked since i dropped it 2 days before (my bad luck) only now it wont even turn on. i've replaced screens before, so is that all i have to do to get it to work? or is there something i have to fix inside the phone. if so, what do i do? i dont want to take it to a technician if i can fix it myself.