Make sure you are using a Nabi charging cable, then try a different outlet, or try using your USB and connecting it to a computer.
If that does not work, it seems that your device might need a screen calibration. To do so, follow the next steps:
Temporarily remove the rubber case.
Hold the Volume+ Button and the Power Button at the same time to trigger a touch screen recalibration.
If the screen is unlocked you will see a message. Follow instructions and please don't touch the screen until the calibration process is complete.
If the screen still does not respond, try performing a soft reset. To perform a soft reset, follow the steps in here: https://www.nabitablet.com/support/artic...