Without a make or model I can't give you specific instructions, but generally speaking your file system is probably damaged, assuming you weren't trying to modify it in any way.
The first thing I would do is to attempt a factory reset through a recovery menu. The recovery menu is usually accessed by pressing buttons in combination. Which buttons and what order will depend on the model of tablet. With the tablet off, you can try pressing both volume keys and the power button and holding them until the tablet powers on and then let go of the power button while still holding the volume buttons. If that doesn't work, try only the volume down button + power or volume down + home + power (assuming you have a "home" button) and only release the power button when the screen blinks.
If you are lucky enough to stumble onto the recover menu you want to find an option that says factory data reset. That will reset your device back to factory specs, but it will also delete user data and user installed apps, so if they are not backed up, they will need to be reinstalled.