So I've had the phone for about 2 days an this happend.
Luckly I had the finger print scanner working so I could still get into it or else I may have though it was dead.
Here's my SOLUTION:
Make sure your volume is up. Play music. You'll notice that the speaker won't work.
Squeeze the screen and back of the phone, just above the volume-UP button. And the music will start playing, and the buttons will now function.
It's clearly not a software issuse so it must be a loose connection from pour quality control. Hope this saves someone hours of googling and frustration.
