Software problem, removal of jailbreak , iTunes error or simple downgrade of iOS, no matter the reason, here is how to solve it thanks to the DFU Mode . Entering DFU mode The DFU (Device Firmware Upgrade) mode is a recovery mode for iOS devices. This mode allows them in case of emergency, to be detected by iTunes for a reinstallation (Downgrade / Upgrade). Turn off your iPhone by pressing the " Power " button for about 4 seconds, then slide the slide . Press the " Home " and " Power " buttons simultaneously for 10 seconds . After 10 seconds, release the " Power " button while holding down the " Home " button . After a few seconds you will see the apple logo appear and the iPhone will restart until displaying a completely black screen. CAUTION : If the display on your device is one of the logos you are in Recovery mode, not DFU . You will have to try again. Your iPhone is now in DFU mode! You can now reinstall iOS in Upgrade or Downgrade mode or restart your device to exit DFU mode . Downgrade your device The downgrade is a process that consists of reinstalling on its device, an earlier version than the one already installed. In the case of iOS, Apple has put in place various security to avoid this. In fact, each version is signed and when a new version is created, the previous version will not be signed in the days to come. [Alert style = "eg white, gray, red, yellow, green" [/ Alert] To downgrade your device, connect it to your computer and open iTunes . Go to this page and download the IPSW file of the firmware you want to use depending on the device. On the iTunes home screen, press the " SHIFT " key on your Windows keyboard (or the " ALT " key on OSX) and click " Restore ". A window will prompt you to select the IPSW file of your firmware. If everything goes well, the restoration of the iPhone starts and it will be operational again under the iOS of your choice. How to put your iPhone 7 into DFU mode Because iPhone 7 doesn't have a physical Home button — it has a capacitive Force Touch Home button — DFU mode functionality has moved to the volume down button. Plug in your iPhone 7. Make sure iTunes is running. Turn Off your iPhone 7 if it isn't already. Press and hold down the On/Off button on the right side of your device for 3 seconds. Press and hold down the volume down button on the left side of your iPhone 7 while still holding down the On/Off button. Keep holding both buttons down for 10 seconds. (If you see the Apple logo, you've held them too long and will need to start again.) Let go of the On/Off Button but keep holding the volume down button for about 5 seconds. (If you see the "Plug into iTunes" screen, then you've held it too long and will need to start again.) If the screen stays black, that's it! Your iPhone 7 should now be in DFU mode. To exit the DFU mode the manipulation is the same as the one presented above to enter. Your iPhone will restart normally and you will have access to all features.