The [Power ON] button won't turn on the device due to a PMIC Hardware lockup.
The PMIC can enter sleep mode under certain low-power conditions, making it unresponsive to communication attempts from the Peripheral Controller (PCon), making it impossible to power up the device.
As a diagnostic response, the PCon provides a visual indication by flashing the green LED in the following pattern:
1 second on, 1 second off repeated 3 times, 3 seconds off, repeat.
Apply AC power to the device and manually force a hardware reset by pressing and holding the [Power ON] + [ENTER] buttons together.