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If the failure to charge is quite sudden, then check
A. that the plugs and jacks involved do not have dirt in them. A scrubbing out with an old (but, clean, and dry) toothbrush would be appropriate.
B. also check that the cords do not have any lumps, or evidence of strain or stress at any point along their length. A wire breaking sufficiently from stress, could cause failure to charge.
The next question about the problem is: How old is the tablet, please?