I have encountered the same problem with my Lumia 950.
I was listening to music while browsing the internet, the battery was around 80%+ charged, and the phone suddenly crashed. (It completely froze, there was no other way to shut it down other than removing the battery, which I did.) After that, the phone now
seems to be stuck in a neverending start loop, the screen stays black and it will vibrate from time to time.
I've tried to reset it (while holding the lower volume button) but it doesn't do anything.
I've tried removing the battery, but it doesn't change anything.
I've also tried to charge it by plugging it to a computer (with AND without battery) but it doesn't get recognized by my laptop anymore. The phone wants to boot, but it will only vibrate once a in a while and the screen will stay black.
I have also tried to reinstall the OS, but since the phone isn't recognized by any of my computers anymore, it's pointless. It won't get detected, and even if it did, there are no files for the Lumia 950 in the Recovery Tool's list...
This phone is only 2 months old and I don't even use it that much. I honestly don't want to buy another one...