First, try to reset the system. This could not be possible, but if you are able to, start with this. To Reset the system you will enter System Settings and then Backup & Reset and you can press on Reset and the system will be resetting to the initial state.
If you are unable to perform this 'soft reset'. you may want to try a hard reset. WARNING: performing a hard reset wipes all data and sets the tablet back to default system setting. To perform a hard reset, push the up & down volume buttons and power button at the same time. When the reset screen comes up, use the volume buttons to choose 'wipe cache'. Then select 'yes', then 'wipe data factory' and 'yes'. After this has all finished, reboot the device.
If the problem still occurs, contact Lenovo support at https://forums.lenovo.com.