There should be categories once you open war3x.mpq with image extractor II or wc3 viewer. If no .blp are under any of them, your war3 may be screwed up or you did not use the tool properly.
The easiest way to find skins for models is with wc3 viewer or image extractor II's tree view list when a mpq archive is open. Re-install your wc3 is the mpq has nothing in it or is not at proper size.