See if you can turn it off. If it allows that, restart it and see if you can get past the screen. It may just need the time turned off.
If it gets stuck again. You can try starting the device in "Safe Mode".
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.
If this doesn't work, you can try a "Factory Reset". It may erase some data though. This can be...