I’m just on my way to bed, so this is just a quick thought. Can you hold your power button for at least 20 or 30 seconds, more if necessary? I have had my tablet act like that, but holding the power button like that will force it to power off – because it really has been on, but not booted successfully after an update, even though it appears off. Then, after doing that, hold the power button for 5 or 10 seconds to see if it will start up – but be patient with it, it might take a LONG time to boot the first time after that.
