Can't log in mommy mode or hard reset

I’m having problems with my son nabi tablet. It won’t let me go into mommy mode doesnt give me the option bar when I touch the little square in the display and it will appear the mommy mode password square only if I press to turn off the tablet or in the back running apps as UI error how can I fix it or reset because I’ve tried to do a hard reset but it won’t give me the hard system menu either only the reboot normal or safemode