I Have a nextbook and it is fully charged however I turn it on and it just flashes. It will not stay on.

You can try do to a factory reset, although that is not likely to work. That will reset the device fully, including deleting anything you have on there.

Hook it up to a computer, if the computer detects it and you can get to it and browse the files on it, then you can see if replacing the screen will fix this. If it does not detect it at all, it could be a system board issue which means time for a new one unless you want to go look for the same system with maybe a cracked screen for cheap and swap screens with yours.