The "Black Models" issue can be caused by many different things. One thing could be the lack of proper lighting in the area. If the world is bright around the model and yet the model is still black: it is a pretty good indicator the problem is the lighting. Check for leaks and whether fullbright is set to 1. Another important note with models coming out back is if you have a 3D skybox in the map. When using a 3d skybox, make sure to have a light_environment both inside the level AND inside the skybox. This is very critical.
Other known causes for Black Models:
0 0 0for the entity it is used in.
- The nearest worldbrush directly beneath the model is either unlit, or using a culled texture such as tools/sky.
In Half-Life 2, black models in-editor are caused by your video card/drivers. This seems to be common with the GeForce 4 series of video cards or very early drivers. They do not appear black in-game.
Also, black models in-editor along with black and/or glitchy 2D-views can be caused by an invalid SteamAppId entry in your gameinfo.txt.