Sounds like it may be a software glitch. There are many things that could cause a software glitch including the maximum amount of memory being used. The simplest step would be to hold the power button to reboot the tablet. If this doesn't work, try connecting the tablet to the charger or a computer and rebooting it again. If the tablet is still unresponsive, push and hold the small reset button on the backside of the tablet until the screen changes. Otherwise, open the tablet and remove and reinsert the battery. There are troubleshooting steps regarding the issue you're describing that can be accessed with this link: Nobis NB07 Troubleshooting.