I also have the same problem , black screen and wont turn on and when i plug it in i get the charging sound over and over again and vibrating over and over again if on mute. when i plug it into my computer it is recognised by itunes so its not a motherboard issue. i have been fixing iphones for over 3 years now and ive had this problem before which i solved by taking the battery out for 10 mins to drain any power that could still be left in the components and it worked fine after that. with this phone i have tried a new battery, 2 different screens so its not a battery or screen issue, i have drained the power from components and tried to boot but nothing. i have my suspicions that it could be a blown backlight fuse which pretty much means its bust but i cant see why this would happen, there must be one more thing that i could try before accepting defeat and taking it into the apple store (which is going to kill me) ??? any more suggestions would be great ?