My nextbook 10.1 windows 8.1 wont turn on its been charging now for more then 4 hours

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.

How old is it? It may need a new battery.

(this is all i could find on the internet so this is not to say it will help you but try it and see what happens).........PRess the power button and the volume down button at the same time and hold until the unit restarts... it resets the charging cycle and the note will charge reasonably quick from then on... I do this on occasion when my battery seems to charge slow.
plus some people are saying get a new charger.

nextbook is showing a yellow light while charging but wont

press power, press home button + volume at the same time a menu should appear in top corner , once that shows leave go of all three buttons then with volume press down and when you reach the heading you need press power . YOU DO THIS ONCE YOUR NEXTBOOK 8 IS TURN OFF ( make sure battery is in ).

send it for warranty repair

Are you sure it's fully charged (like for 12 hours)? If so, try holding down the power button for at least 10-15 seconds, maybe more. Sometimes that works.