For what my experience indicates is a hardware problem, usually logic board went bad. try with other logic board if you can get one from a friend's iPhone.
Trey i have the same problem as dk7250 i tried the suggestions but didnt work out. could you try explaining how to do the reset pin procedure please. i am a techie. Thankz
Bobby can you post the exact orientation of the ground part, thanks
In step 23 the battery screw is not 1.6 mm its a bit larger, bit carefull!! Put it in the right order!!