All i Phone or i Pod Touch settings are restored to their factory condition. First thing to check is to make sure you have the latest version of i Tunes installed on your Mac or Windows PC. When your phone is detected, select it in i Tunes under the list of devices.
If your i Phone is not responsive and i Tunes does not detect it we must put your phone in DFU mode.
*If you are jailbroken, it is my personal opinion . Select the Restore option when i Tunes prompts you.
Once the restore process has completed your i Phone will restart and the Apple logo will appear while booting up.
Maybe you jailbroke it and things did not go as well as you planned?
Perhaps you have to take your i Phone back to an Apple Store because of a hardware related issue and you are jailbroken?
If that doesn't help, I'd try a different computer. I tried it using my friend's desktop and after a few tries it worked. After I installed and Ccbackground on my jailbroken 6 plus, Siri only works after rebooting my phone, than stop working moments later.
You can follow through the wizard and get access to your device where you find yourself on the same firmware version but with stock setup without losing jailbreak ability as you are on same firmware version which you were previously jailbroken.
Meaning that you can actually get back to jailbreaking once again if you wish.
As you all know by now Apple has stopped restore of i OS 10.3 and 10.2 update making it impossible to downgrade and jailbreak the devices.
There are several other apps and tweaks available such as Cydia Eraser tool – offered by Jay Freeman – brings the ability to restore back to a stock version of i OS without actually having to upgrade from a firmware that was able to be jailbroken.