Screen problem

I was using my LG G3 as usual, just watching some video's, when the screen began to randomly black out. I thought nothing of it, and continued to watch video's. This happened twice. Then next thing i know, the phone's screen permanently off, and it wont light up. The only exception to this is when i plug the phone in to charge without a battery pack in. When i do this, the screen is still black, but is powered. I haven't done anything unusual, like rooting the phone, and i can still accept calls on it, and change the volume. If anyone cold help, that would be great, anything at all.

Thanks