Try a Hard Reset, hold a same time both Home and Power buttons for about 15 seconds until iPhone restarts. If this does not work then, connect the iPhone to Computer launch iTunes, does iTunes recognize it? Flip the Mute/Vibrate switch up and down does the iPhone vibrate? If yes to either then possibly Cable #1 is not attached properly. If no to both then possibly Cable #4 is not attached properly. If these all fail, then you could try a DFU restore, connect iPhone to computer, launch iTunes, hold Home and Power buttons together for exactly 10 seconds, release Power button, keep holding Home button for another 15 to 30 seconds, see if iTunes recognizes iPhone in Recovery Mode.