using cs 5.5 btw
It's likely that, when you add your camera, your layers are not positioned within the camera's field of view for some reason. Are you viewing using the "Active Camera"?
Try setting the viewer temorarily to "Top View" and assess where your layers and camera are in 3D space. Is the camera pointed toward the layers? Are the layers oriented toward the camera?
Do you have lights in your composition? If you do, and they aren't hitting your layers properly, the layers may appear black.
Working with cameras and lights in AE is like the real world. You need to know where your layers, cameras and lights are in the "room", and make sure they are pointing in the right directions etc.
If you are in a custom view and you add a new 2D layer it will not show up. Switch to Active Camera and the layer will be there.