You may encounter the following symptoms while updating or restoring your iPhone or iPod touch:

iPhone or iPod touch continually restarts but never displays the Home screen.
An update or restore did not complete and the device is no longer recognized in iTunes.
iPhone or iPod touch stops responding, showing the Apple logo with no progress bar or a stopped progress bar, for over ten minutes.

If this occurs, you can place the device into recovery mode and attempt to restore the device again. If iTunes displayed an alert with an error code, see this article before attempting the steps outlined here.
Note: In certain situations, an iPhone or iPod touch will automatically go into recovery mode after an update or restore issue. If your device is already in recovery mode, you can attempt to restore using iTunes.

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4. iTunes: Backing up, updating, and restoring your iPhone, iPad, or iPod touch software
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