Hi,
Has the tablet been dropped or gotten wet at all?
Try disconnecting the battery, then hold the power button operated for about 10 seconds before reconnecting the battery, to see if this will reset the tablet. At least enough to be able to hopefully do something more to resolve the problem.
Here’s a link to the ifixit RCA RCT6773W22 Battery Replacement guide, which may be of some help. You do not have to remove the battery, just disconnect it from and reconnect it to the systemboard. You’ll need soldering skills and tools (or know someone who has) to do this.
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