Error code (-39) when trying to restore iPad Mini 2.

Well, error 39 is not listed in the standard update/restore error list. Get help with iOS update and restore errors - Apple Support However, it is in sequence with many of the hardware errors. You can look up those numbers close, i.e. 36, 37, 40, and see if any of that troubleshooting helps. Otherwise, you will need to make an appointment at the Genius Bar of the nearest Apple Store to have the device looked at.