Has the tablet been dropped, banged, sat on, etc.? If so that could be the problem. Even though you see no physical damage, that doesn't mean something inside didn't get jarred loose or disconnected. Also, sometimes displays just go. It happens.
If it is the part needing to be replaced, if the device is still under warranty, then you should contact the manufacturer. If it isn't under warranty, then you have the option of trying to replace the display yourself, or taking it to someone/someplace that can.
But before you resort to replacement, try starting it in "Safe Mode" and see if it lets things work. If it does, then you probably have something on the device that is the problem. A bad app or a bad app update, that you need to remove to resolve the problem.
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.