Never bothered to post a comment on such site but iPhone is something else and want to share my experience and what worked for me.
Came on this page looking for help thru google on the subject of this thread but my problem or situation appeared to be relatively unique/weird. So here are the details:
My iPhone/problem: 4S, locked to a UK service provider (T-Mobile), got unlocked thru GeVe insertion/sim; was using Facetime when dropped with 60% battery remaining, dropped it from a height of about 4.5 feet on a hard tiled floor with significant impact. phone immediately went dead with black screen and without any crack of scratch on the front;
Solution: came on this page looking for a possible solution, tried various ones including the one mentioned by Taseraq (so far the most popular one on this thread!) with various time-duration combinations; no results......:(
Then attached the phone to computer, a bit weird looking battery sign appeared on the black screen and immediately disappeared, pressed on/off button but no life in the phone yet, again checked after about 6-7 minutes, battery charging sign would appear for a moment and screen would go black/dead again; left phone in this condition (connected to computer (until now charged only about 3% during all this time!)) for a total time of about 15 minutes; suddenly familiar Apple sign automatically lights up the black screen and I am back to life..........but not yet......as it wont connect to the my current network I am using and keep on searching and searching.
For the final push; removed the SIM along with the GeVe and inserted it again and it got connected to my current network within seconds!
My assessment/conclusion: the sudden drop impact caused the more than 60% remaining batter to drain to the hilt eitherdirectly or indirectly thru interference with the software.