Hello,
 
 I tested your cube and its full or errors (Object i tested is on this link 
http://supervision2.filnet.fr/froggy/ftp/obj/c1.3ds).
 
 
Major Problems
  - It is setup to "editable mesh" when it should be setup as "editable poly".
  - Your 'cube' have 14 vertices, how come ? A normal cube should have onle 8 vertices (one for each corners).
 
Minor Problems
  - Its not a cube, more a rectangle :p
  - No texture attribued
  - Rendering method is phong, i'll rather go with blinn