Try turning it off and then start it up in "Safe Mode". If it will load fully (although your access will be limited) then you probably have a bad app, virus, malware, etc., on the device that will need to be removed before you can load it up normally. Once it has been removed then just restart the tablet to get out of "Safe Mode".
Now, if it still won't start up fully in "Safe Mode" then it could be a more severe software issue, requiring you do a "Hard Reset" of the device, or even a hardware issue.
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...