It sounds like you're using 3 textures, with the alpha on the 3rd texture. As I recall, you use 2 textures, color map and Normal map. And you put the alpha on the first one--the color map.

If they're pitch black, that's strange. Normally, you always get at least a bit of specularity. Make sure that you're light object is very close to the object with the Normal Map.

I often had an easier time trouble-shooting when I had zero normal lights in the scene. Just the Per Pixel dynamic light.