Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
Does the problem happen when your tablet is connected to a charger, and you press and hold the power button?
It it still occurs when connected to a charger then you will need to try a factory reset.
A factory reset will erase all your personal data.
You can do this from the Android Recovery Menu:
Press and hold both the "Volume Up" and "Power On" keys until you see the Android logo.
Use the "Volume Up" and "Volume Down" keys to navigate through the menu, and use "Power On" for OK.
Choose "wipe data / factory reset", then "yes erase all data," and reset the tablet.
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