My iphone 6 went black last night
Took following steps :
1. Chrged it for one hour - did not work
2. Tried to turn it on - did not work
3. Connected to PC and tried to see in iTunes to restore - did not work
iPhone 6, iOS 8.3
once you go black you never go back
but try If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support