Put iPhone Into DFU Mode In some situations, your iPhone may not turn on because it won't boot up. This can happen after jailbreaking or when you try to install an iOS update without enough battery life. If you're facing this problem, put your phone into DFU mode this way: Plug your iPhone into your computer Hold down the on/off button for 3 seconds, then let it go Hold down the on/off button and Home button together for about 10 seconds Release the on/off button, but keep holding the Home button for about 5 seconds If the screen stays black and nothing appears, you're in DFU Mode. Follow the onscreen instructions in iTunes.