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...