A friend installed "Installer 3" on my iPhone with a bunch of 3rd party apps. The reason I let him do this was because he said that I could simply click "restore" on iTunes and it would go back to its original state. Ever since he did this, my phone has been randomly shutting off, the screen has been flickering, and I don't really use any of the 3rd party apps anyway. I want to go back to having a legitimate iPhone, but when I click restore on iTunes it recognizes a problem with the firmware and will not restore. How do I completely erase everything from my iPhone and restore it to its original state?