Try starting it up in "Safe Mode" and see if it will load. If it does you won't be able to do most things, as it is a restricted mode, however, this means it is probably a bad app(s), bad app update(s), malware or a virus on the device that needs to be uninstalled/removed. One the item(s) are gone, then restart the device and it should load correctly.
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...