iPhone Black screen of death

Hold the Home and Power buttons down at the same time for up to 30 seconds (no kidding) until the Apple appears. Once it displays, the reset is in progress and the Slide to Unlock screen will display shortly.

Cheers,

GB

It seems to me you have done almost everything you can, first I would try and doing a longer hard reset than just three seconds, but you can also try to put your phone in recovery mode if nothing else works. You do this by plugging you phone into your computer and following these steps. hold sleep/wake and home button for 15 seconds, then release the sleep/wake button. You won't be able to tell if it works until a prompt on iTunes tells you your iPhone is in recovery mode. Hope this helps, best of luck to you

~Michael M

But do you have any indication that it is actually charging? If the device isn't getting charged because of debris in the connectors, then you could have the same symptoms.

If you are not sure that it is actually charging, clean out the connectors with a soft, clean toothbrush, or very carefully, with a toothpick.

Once it has been cleaned, plug the device in again to be charged, and give it 5 minutes or so to see if the battery signal displays with the little red line.

Cheers,

GB

I had this exact same issue with my 5C this week and no amount of holding the buttons made a difference. In my case I had to take it to apple who said it was a software issue, but once the phone was back up, it now won't connect to the server, so am still waiting for a fix from Apple now. Unfortunately you may need to see the pro's for this one.

Are you certain that it has a charge?

Cheers,

GB