A similar situation encountered with a friend's Nextbook. The on/off switch or connection was faulty. I replaced the switch and it works fine now. This may or may not be the same situation you are encountering. To correct the situation, requires some electronics knowledge,a digital multimeter, set of small flat-head and Phillips screwdrivers, soldering "know-how" and most importantly, plenty of patience. Also getting the case opened as well as resealing requires following different sequence of events to ensure proper seating and not damaging the case. It took me a couple of times to reopen and reseat the case because one exterior button was not actually touching the button on the circuit board.
Perhaps an electronics repair place may be able to help if your device is out of warranty or you don't want to get involved with a tedious repair task. Otherwise, you may be able to search for repair parts and perhaps the electronics repair could install them (most likely with no guarantees).
I hope this helps.