dropped phone black screen and unresponsive

I have an iphone 5c that I am trying to fix for someone. The phone was dropped and the user reported that the display showed numerous lines and the went black. The phone doesn't appear to have any other responses either. You can't call it or get it to vibrate by messing with the volume. I have tried the hard reset with no luck and I have also opened the phone and disconnected the battery and the digitizer and lcd connections and then reconnected everything just in case something had come loose during the drop. I have the same results. I have tried hooking the phone up to a computer as well and it was not recognized as being connected. What could be the problem? Any suggestions to determine the cause?