I am trying to fix my friend's AT&T iPhone 4. Whenever I turn it on it goes to the apple logo, then the greenpois0n logo and the spinning wheel freezes. This goes on until it dies (the phone is on low battery) or unless I hold the home button and it goes into recovery mode. I have it plugged in and when it does it just charges enough, boots up, and does the same thing. I have been unable to get it into dfu mode, only recovery. It is plugged into the computer and it is not detected at all. It had 4.1 fw on it. Is there any way to fix it?