If your iDevice starts acting strange and you've gone through the normal fixes, the recovery mode might be the answer. So you can just reset the device and reinstall iOS with iTunes.
When you reinstall iOS, there is a possibility that all data on your phone will be lost. It is therefore advisable to make regular backups of your computer via iTunes or iCloud. To start your iOS device in recovery mode:
First, make sure you have the latest version of iTunes
. First, make sure you are using the latest version of iTunes. With the application open, go to iTunes> About iTunes.
Make a note of the version you are using and compare this official Apple support page with the latest release version.
If that's not possible, you can get started. The rest of the process varies slightly depending on the device used, so we discuss each one individually.
For iPhone 7 / iPhone 7 Plus or later
If you're using an iPhone 7, 7 Plus, 8, 8 Plus, X, XS, XS Max, or XR is the following to do.
First, make sure your phone is turned off. Then press and release the volume up button.
Then immediately press the volume up button and release it.
Now hold down the side key, the only one on the side opposite the volume keys. Do not release the button even if the Apple logo flashes on the screen. Hold down the key until the recovery mode screen is displayed.
When this screen appears, continue and connect your device to your computer using a Lightning cable.
For iPhone 6s or earlier Most iPads
This guide is for iPhone 6s and earlier models and most iPad models except the iPad Pro 11 and 12.9-inch. Look at the next section for these two.
First, make sure your device is turned off. Then press and release the volume up button.
Then press and hold the Home button and the Standby button. The Sleep / Wake button is located on the iPhone 6 or later users page, and the iPhone 5s and earlier on the top right. Do not release the buttons even if the Apple logo flashes on the screen. Hold down the button until the recovery mode screen appears.
When this is displayed, connect the device to your computer.
For iPad Pro 11-inch or iPad Pro 12.9-inch  Press the volume up button momentarily and release it. Then briefly press the volume down button. Press and hold the standby button on the top of the device until it restarts. Press and hold the standby button until the iPad enters recovery mode.
When the recovery mode starts, connect the device to your computer.
What to do if you are in recovery mode  Now that your device is in recovery mode, you have about 15 minutes before it automatically shuts down. If you are not moving fast enough and the device is leaving recovery mode, repeat the same procedure as described above to recall it.
A window like the one below will appear on your computer as soon as you have successfully completed the restore mode on your phone or tablet. If you see the "Restore or Update" options, choose "Update."
You should try "Update" instead of "Restore" because your problems may be resolved by a simple update iPhone that stores all content and personal settings. If that does not work, you may need to select the "Restore" option, which will erase all content and personal information on your device. Do not accidentally click "Restore" if you do not have a proper backup of your data or want to go through this process, and make sure that you first try "Updating" to save yourself a potential problem.
Select "Refresh" And then iTunes will work to reinstall iOS on your phone while preserving your data. When the update or restore process is complete, you will be asked to set up your device.