If your restoration attempts using iTunes or apple configurator have failed you may have some luck trying a DFU Restore. This can also be helpful if your iPhone doesn’t turn on, charge or it won’t go into recovery mode.
Doing this will wipe all data from your device so make sure you have a working backup somewhere. Hopefully you have done this before the phone stopped working, right?
If you successfully want to do this procedure timing is essential. I recommend you use a stopwatch to time it right. Use the stopwatch app on another phone for example.
How To DFU Restore your iPhone (including iPhone 7)
1. Charge your iPhone for about 5 – 10 minutes then connect it to a computer running iTunes.
2. Press and hold the following buttons for eight seconds, then release only the sleep/wake button.
- iPhone 7 – Sleep/Wake and volume down button
- iPhone 6s or earlier – Sleep/Wake button and Home button
3. Keep the home button (or volume down on iPhone 7) pressed until you get the Recovery Mode prompt in iTunes. This could take 30 seconds or so.
In DFU mode the display is supposed to be blank. If it lights up repeat the above instructions and make sure you time it correctly. If you time it wrong, it won’t work.
Normally you shouldn’t have to do a DFU mode reset. When you do a regular restore though iTunes it removes all personal data and media. But the basic iOS firmware is still on the phone. When you do the procedure above it also removes this basic iOS firmware and reinstalls it. In some cases it can help waking an dead iphone up and getting it to work again.