Why isn't my tablet charging?

Ok so my tablet stopped charging all of a sudden about a week ago (2-15-16). It wouldn't charge until it went into sleep mode (left alone). It would charge with the red X through the battery. But now as of 2-19-16 it won't charge at all. It starts to charge then stops, goes black, then starts again. I've tried holding the power button and adjusting the charger but so far nothing works. The charger is brand new so it can't be it.