Well, you could try starting it in "Safe Mode" and see if it will fully load. If it does, then there is an app, virus or malware on the tablet that needs to be removed to be able to start it in normal mode.
If it won't start up in "Safe Mode", you may have to do a "Hard Reset". However I would save that for a last resort as it will wipe all your personal data (photos, music, contacts, apps, etc.)
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...