Same thing happened to both my grandsons' N7S Pros. I had to open the tablet (see Youtube for instructions) and carefully inspect the underside of the circuit board where the charging jack is mounted. The center pin had broken loose and needed to be carefully resoldered to the board. This procedure may be beyond the capabilities of many users. You'll need soldering skills and proper tools. If you're not comfortable with this procedure it's probably best to contact a repair center.