Moreover, in this case, you'd better reset the iPhone accidentally, and the common method is - press and hold Volume Up + Volume Down simultaneously until you see the Apple logo connect to iTunes and attempt to restore your iPhone
Now the dilemma would begin. After you connect to iTunes, it will start restoring the firmware. At first, the restoration will succeed but it will show an error code of something like "Error 9 or something like this". If you are also unlucky, the iTunes will stop restoring iPhone for a while without any word or signal.
After you connect it again, the firmware is based on your last successfully used firmware, it needs to check and confirm that you still had the right firmware for your device. If it doesn't work, it will display an error code, and you may get a message that something is not right.
In the case of iTunes error 9, you need not bother about the error. But if it appears several times without any opportunity to recover, and it starts again and stops, sometime, a message will appear under error 9.
The warning message "unknown error occurred" is seen when iTunes detects a problem with iTunes database. This happened when iPhone restore failed hangs with 0% progress of completing restore. You may need to restore your device many times until you finally get iTunes to work again. If iTunes cannot detect the problem, you may try to quit iTunes or restart your computer. If that does not work, you may try to do a factory reset on your iPhone and restart iTunes. If still no luck, you may need to try some other recovery methods to recover iOS device. If system restarts and there is no problem with iTunes, it may be an iTunes related problem, which can be fixed by some simple steps. You can visit this article for better solution. d2c66b5586