Hmm... I can only think of two things... 1) Is the ground plane actually turned on (I know that seems really simply, but you never know)? 2) Are any of the lights pointing to where they would cast a shadow on the ground? Try starting a new render. Turn on the ground plane, load a box prop, and move it so that it is off the ground. Delete all of the default lights. Create a new light, make sure it's a spotlight, then set all of it's trans and rotate parameters to 0. this should let you see the outline of the spotlight in your window. Click the spotlight, and go to Object(I think)->Point at. Point it at your box... then move the spotlight up on the Y until it's above the box and shining light down onto the box. Try rendering that... it should cast a shadow onto the ground... this will at least let you see if there's something really wrong, or if you just need to fiddle with where the lights in your scene are pointing. I hope that helps...