First, attach the phone to a PC, and then turn the phone off. Next, hold the power and home buttons simultaneously for 10 seconds. Finally, release the power button while still holding down the home button. The PC recognizes the device in DFU mode, while the phone display stays off. If this method isn't working, attempt the same process with less time holding down the home and power buttons.
Hook up your phone to a PC. Next, hold the home and power buttons. The phone should turn off at this point. Keep holding the buttons down for around 10 seconds, but make sure the phone doesn't turn back on. If it does, try again with less time. Finally, release the power button and hold the home button until your device is recognized by the PC. This method can cause 1604 errors to occur.
While the phone is attached to the PC, turn it off. Next, press and hold the power button. As soon as you see the display on the screen, press and hold the home button. The display should disappear. Hold the power and home buttons simultaneously for at least 10 seconds. Finally release the power button and hold the home button until the device is recognized on the PC.