iPhone 6 stuck on spinning wheel under booting

Hey

-- BACSTORY, MAY NOT HAVE ANYTHING TO DO WITH ANYTHING -- I changed my friends screen and battery a while back, and everything worked fine - he then dropped it and the the two plastic mounts, the hex bolts holding the screen in place screws into snapped off. So the screen couldn't be held down. He decided to use it anyway.

Then the problem:

Suddenly while using it, it decided to reboot, but under booting up it would just stay on the apple logo and then go out saying it had to be charged - when in a charger it kept buzzing(two buzzes like when you plug in the charger) on the apple logo. I thought it was battery related, so I plugged in a spare one, and it went to that spinning circle instead but still buzzing and not going any further. I tried with another screen, and still the same. The coumpuer sees it as a functional phone as iTunes askses for a password on the phone to access it, but since that's stuck on the spinning circle, I'm not able to reset it.

I can't force reset it in third party app since it's seen as a functional phone.

Any suggestions?