Try turning it off. If it won't power off, then wait for it to run out of power and plug it in to charge. Leave it off for a short while, so it can get enough of a charge for a short turn on. Once it has charged up a bit then try turning it on. If it works fine, great, charge it some more and you are good. If it doesn't work still, then you will need to again turn it off and give it a small charge. Then try turning it on in "Safe Mode". Should it load fine in "Safe Mode" then there is something on the tablet that is interfering with its normal operation. You will need to remove whatever it is. Virus, malware, bad app, 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 disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.