check your layer combination !
Mybe some of your layers go off in 3d ! (this is common reason for your problems)
Do u see everything when u make section ?
Select on plan what you want in 3d, with marquee tool and then go to 3d
If you still cant see it, then select one object, go to 3d and u should see only that object and then select Show all in 3d.
But first off all CheCk your Layer Cobination !