Faulty cable, USB port, or driver issue. Solution: Use a different USB port or cable. Restart your computer. On Windows, reinstall Apple Mobile Device USB driver via Device Manager.
A failed jailbreak attempt had left the device in a "boot loop" limbo. It wasn't dead, but it wasn't exactly alive. To save it, Leo knew he had to go deeper than a standard restart. He needed to enter the digital basement of the iOS architecture: (Device Firmware Update). How to Open DFU Mode on iPhone 5C