[Help] Battery or Logic board?

I left my phone to charge via USB pc port. When I woke up, the screen was showing me the Bootlogo (Unlocked bootloader warning bla bla bla). So I disconnected the X and tried to reboot it and now it won't "wake up". Not even to fastboot. I tried all the keys combinations, for short and long time pressed. Nothing. When I connect it to my computer and hold the power button, the green LED blinks once and the computer makes the "Device connected sound" but after a few seconds, the disconnected device sound kicks in. Did this happen to someone? Did my battery died? Or my entirely phone did? Thank you.