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.
Check to see what material has been applied.
Click the part, select the Appearance icon (the multi-coloured globe) and click all the red X's to remove all appearances.