Ive been trying to call customer service and can not reach anyone! my sons nextbook8 keeps shutting off even tho fully charged

Sounds like a defective battery! I'd contact the manufactuer's Custom service and ask them to replace your battery, there's a good possibility they will, and most likely for free or a minimal charge. If it's fairly new take it back to the store and exchange it, but the manufacturer will be a good bet if that's not possible, it may still be under warranty! Thanks and have a Great Day! Best of Luck! See picture below please!

Hold the volume UP botton down when it is OFF, then while holding that button down press and hold the power on button and keep both pressed for about 10 seconds. Then release.

Don't know if this will work but put it in a cold place for couple days then re-try, don't mean freezer tho lol.;

Good evening
This happened to my iPad. When I discovered that there were many programs open, I closed them and it charged.
hope this works for you as it did for me. Some one told me that it was a good idea to plug the tablet to a computer and charge it that way.
kolbrun

Almost everyone knows who makes the best..... Not that any brand is perfect. But people still persist in buying the cheapest. I know this doesn't help your current predicament... but you have to think before you buy! I've had 3 iPads now and none have had anything like what your describing.
Good Luck in with your future purchases.

There maybe a tiny pinhole Reset button on the back of the tablet. Use a straightened paper clip and insert it into this pinhole.