Some video cards are affected by how Morrowind handles a fog density setting of zero in interior cells with the result that the interior is pitch black, except for some light sources, and no amount of light, night-eye, or gamma setting will make the interior visible. This is known as the fog bug.
Originally this only affected ATi (since bought by AMD) graphics cards. It was referred to as the "ATi Fog Bug" and mods such as Sotha Sil Dome of Serlyn fix by Kane were created to fix the bug.
Mod users can use tes3cmd to create a multipatch which will fix the fogbug if present in any of their loaded mods.