In case you don't know the password, I advise you to perform a reset operation for the settings. When the password prompt appears, simply enter the password four times in a row, then the tablet will suggest you Reset it. Once you do that, the password will be removed and you will have access to your device.
Please notice that performing the Reset will also delete everything stored on the device, but that's not to worry as you can restore them back if you purchased them.
