No matter what I do the device will not turn on. What should I do to fix this?

It seems like your device is frozen. Try to hold down the power button until the screen turns off. It usually takes like 10 - 20 secs for it to power off. If that does not work then you could try to wait until the device runs out of battery and shuts off on its own. Then you would have to charge it and then try to turn it back on and see if that works. If you have any other problems with your Nabi Jr you can go to this link to fix any other problems.