Set your rendering type to Textured. This will show holes in your model where there are backfaces. Go into edit mode, click the face select button on the bottom of the window, and select the faces that are backwards. Hit Ctrl+f, and then (at the top of the list) choose flip normals. This SHOULD fix the shading, though I have had it once where it did not, it works 99.99% of the time.
If it doesnt work, remove the UV map and retry from there.
If it STILL doesnt work, Spawn a cube, select it, and then select the messed up part of your model. (THE ORDER MATTERS, SELECT THE CUBE LAST.) Hit Ctrl+j, then try the above procedure again. If there's any holes, reverse them. This is all I can think of to help you, so sorry if Im useless.
