If your device is not plugged in using the VTech® recommended Power Adapter, then your batteries could need replacement. Check to see if your AA batteries aren't depleted. Try plugging in your device using the Power Adapter. One of these suggestions should help you with this issue.
If you plugged in your Power Adapter and you're still not able to turn on your tablet, then you might have an issue with that Power Adapter or with the power connecting port on the device. Consider replacing the power adapter or replacing the power connection port. If you replaced the batteries with working batteries and your device is still not powering up, then you might want to consider replacing the circuit board.