First, try turning off your iPhone, and powering it back on. This probably won't work.
Second, Try Recovery mode.
(Recovery mode erases your device and restores it, which should resolve the issue. If you previously synced with iTunes or iCloud, you may be able to restore from your backup after recovery.
1. Turn off your device. If you can't turn it off, press and hold the Sleep/Wake and Home buttons at the same time and wait a few seconds for it to turn off.
2. Plug the device's USB cable into your computer only.
3. Hold down the device's Home button as you connect the USB cable to it.
4. When you see the Connect to iTunes screen, release the Home button. If you don't see this screen, try steps 1 through 3 one more time.
iTunes should open and display a message such as: "iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes."
5. Use iTunes to restore your device.
Third, Try DFU mode.
How to enter DFU mode:
1. Plug your device into your computer
2. Turn off the device by holding the Sleep/Wake or Power button and swiping it off
3.Hold the power button for 3 seconds
4.Begin holding the Home button without releasing the Sleep/Power button for 10 seconds
5.Release the power button and continue holding the home button until you get a popup from iTunes that your device is recognized as being in recovery mode.
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