How to fix an unknown error occurred (4014) (Nothing else worked)

Consider restoring your device from DFU (Device Firmware Update) mode as a last resort, as it involves data loss, and only after you have verified that there is nothing wrong with your USB lightning cable and the computer. The procedure you need to follow is described below:

1. Put your device into DFU mode - consult this article on Apple, if you are not sure how;
2. Connect your device with your computer, through the USB cable;
3. Restore your device, following the on-screen instruction on your computer.
   
   

Note: If you use a laptop, make sure to plug it in the power adapter first, as interrupting the restoring process is not advised and can be dangerous for your device.

If none of the other solutions worked, and the error message 4014 persists, try restoring or updating your device from another computer, because something may be blocking your current computer to establish link with your iOS device. 

Follow the tips in the video below, if you aren't sure how to restore your device, through iTunes.

Lightning cables aren't immune to time and usage. If you use it correctly, you can just use it more time, but the time will come when you need to replace the cable. If you updated or restored your device successfully, by using another USB cable, your USB cable was most certainly the reason for the an unknown error occurred (4014) error message, and you need to buy a new one.

Note: Make sure to buy an original USB cable from authorized stores only, to prevent the future errors that may arise.