I know these replies/questions are year (s) old but i just replaced a battery in my Iphone 4 and got the same issue on/off button no longer worked. Took back off again and theres a little tab (hooked upward tab) that is under one of the 2 screws you remove to detach the battery cable/connector. Just rebend that curved end upwards so when you close the back to gether again it will touch its grounded location. Now my issue is trying to replace the screen, all videos on YouTube are of a 4S and the parts are not the same i went as far as the speaker removal and the videos got different so i closed it back together. I know my simple 4 is OLD but it works for me. Hope this helps someone.