I had the same problem with my nextbook nx16a11264xd. I was using a universal charger with selectable voltage/polarity. I finally decided to open the case and check the batteries voltage. I unplugged the batteries connector and tested the voltage, to my surprise the multimeter read 4.16V. I reconnected the batteries, snapped the case back on and I was surprised once again the tablet now charges. It also stays on when not connected to the charger. I can only imagine by disconnecting the batteries was similar to a hard factory reset (this is done with the power off, hold the volume up button then press and hold the power button for 5-7 seconds). Also make sure the charger you are using outputs 5V and at least 1500 mA. This post is probably too late to help you but hopefully it will help others with this problem.