Device randomly shut off, wont respond to charger.

So, I was using my oneplus one and it randomly shut off. It wont respond to anything. That means, double taps, any gestures or plugging it into a charger or computer. I know I had enough battery to last about 5-6 hours. It charged just fine. My power button and volume buttons dont work. I think I messed them up while I replacing the screen. Weird thing, the power button worked when I made the switch so I was able to turn on the phone but then just stopped working after it like literally 10 minutes later. I could order another battery, volume and power button. But, I dont know how to replace the volume and power button. ANY type of help would be greatly appreciated!