Aporte original por: Grace ,
Connect your device to your computer and then launch 3uTools, and check what mode your device is in as the following picture. And you could manually enter dfu mode or recovery mode. [http://www.3u.com/tutorial/articles/37/how-to-put-your-iphone-in-dfu-mode-and-recovery-mode|How to Put your iDevices in DFU mode, Recovery Mode and Normal Mode?] Then you can restore it on 3uTools, if there is no hardware issue on your device, you can successfully flash your iPhone.