I am running 2011.  My parts are all transparent,even though I have everything set to shaded that I can find. Is there a setting somewhere that over-rides the

display state ?  This also effects my assemblies. As I am rotating my parts, they disappear until I let go of the mouse.   When I hold down the mouse wheel to rotate the parts, It is correctly shaded, but as soon as I let go of the mouse wheel , they go back to transparent.