Just solved this same problem. The battery is completely dead. I had to use a power bank to provide power fast enough to turn the phone on into recovery. I then wiped the cache and data partitions and factory reset it. It would then start to boot and turn off after a few seconds as if the power button was being held. I was able to get pass this by continuously pressing/releasing the power button. It turns out that there was a short in the power button and would shut the phone off and try to turn it back on immediately, completely draining the battery even with the charger attached. Even with the power bank attached, the phone continued to power cycle, but the power bank provided enough power fast enough to allow the phone to keep cycling until the short resolved. It was probably due to some water getting into the power button after applying a soft screen protector.