Why does my tablet not turn on sometimes?
It has been frequently happening among a myriad of other problems.
You could have a bad battery, faulty charger, faulty charing port, software issues or a bad motherboard. Try to see if the charger is bad by using another charger that is compatible with your device or check to see if the charging port is not obstructed by anything. If you're still having issues you can take a look at this site; it will show how to replace the battery if that the issues or the motherboard.