It may be that your normals are reversed and you have single-sided lighting selected. The lighting option is in your model pane - it's a check-box called "two-sided lighting". If you don't have that box checked, you have single sided lighting, the side opposite the normals will appear black.
Might also be a disconnect between your model and the shader, but I doubt it. you can try re-assigning the shader or assigning a new one - but it looks like the lighitng is your problem.
