Install the latest version of iTunes.
Restart your computer.
Check for updates to your Mac or PC. If you restart your computer for an update, check for updates again after you restart.
Try to restore your device using another USB cable.
Try to restore your device on another computer.
Force your device to restart.
If none of these work contact apple customer support, as it says here
https
/support.apple.com/en-gb/HT201444
Hope this helps