Hi there my friend sold me an iphone 4s however it is stuck on an constant apple logo loop. I have tried restoring it in dfu mode and recovery mode however non of this has worked. every time i restore it gets to the point where itunes is waiting for the phone to restart but it just goes back to the logo loop and says error 4013. I have tried tiny umbrella and redsnow however neither of these tools even detects the iphone any help would be much appreciated.