It sounds like something you recently installed or downloaded is messing with it. The first thing I would suggest is trying to start it in "Safe Mode". If it starts up this way, then it is definitely a problem with an app or downloaded software. You would then need to determine which one it was. Any software/apps/files/updates just prior to the problem would be serious candidates.
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 safe mode, simply repeat the steps above, and you should see "Safe Mode: Off" rather than On.