Is this "Android TV box with an internal 2TB hard-drive" some sort of DVR device? The hard-drive could be in a Linux format, e.g. EXT2, EXT4, or is likely to be in a completely proprietary format, and your PC(running Windows?) can't read it. You could try booting with a live Linux OS, see if it will read then. Even then the stored videos could be in some proprietary format.