Well you can try loading it in "Safe Mode" and see if it will fully load. If it does, then you probably have something (malware, virus, bad app, etc.,) on the tablet that needs to be removed. If it won't, and keeps being stuck, then you may well have to do a "Hard Reset".
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.
NOTE: Doing this will clear 'all' the...