display 3D objects

Hi all, I''m trying to use 3dsMax5 to create some 3D models and use a VC++ & directx program to display it. I''ve draw a plane in 3ds, it could be displayed in my program. But when I''ve added a small cube on the plane, only the cube can be displayed, the plane disappeared. Why? I exported the models into a .3ds file and then converted it into .x file by conv3ds.exe. The plane is 30000x30000 units in 3ds at (0,0,0) and the cube is 3000x3000x3000 at (0, 5000, 0). If only a plane is exported, the whole plane could be seen. Help~ Thanks ~nobird