I have tried all of the solutions here, apart from the one about jump-starting the battery... because my battery charges fine, yet the device doesn't power on regardless. I accidentally figured a way to power on the device with 100% success, but first some basics: (1) Make sure that the device has at least 2% or 3% charge, enough to be able to boot up normally, leave it charging for 30min. if you're not sure; (2) You will need to have a charger to do this "trick" (either wall charger or USB charger). Now, follow these steps very closely: (1) Press and hold the power button and plug the charger in, but do not release the power button; (2) The charging icon should momentarily appear on the screen, as soon as it disappears unplug the charger while still holding the power button; (3) Wait around 3 seconds and Google's logo should appear - at which point you can let go of the power button.