I'm having the same problem as most, I just replaced the screen although it had broken a long time ago 1-2 years maybe. I wonder if that has something to do with it. Anyway it won't turn on, won't charge, won't be recognized in iTunes and noting happens when I attempt to put it in DFU mode. I tried grounding the battery terminal and nothing happened. I think that all cables are attached and nothing is loose. Any suggestions?