iPhone 6 won't turn on after ios 8.4
After updating to ios 8.4 it did turn on well,. everything was ok , it had like 60% battery, it was connected while it was updating the ios,. I went to sleep last night and today in the morning the iPhone it's dead, not responding at all, black screen, no logo or nothing, I already tried hard resetting the iphone, power b + sleep b. connected or disconnected, plugged to my pc, and nothing, what else can I do,. I already have an appointment for tomorrow, but, in the mean time, , thks.
iPhone 6 Plus, iOS 8.4