I have downloaded and installed Sweet Home 3D (W7, 64bit, 4GB RAM). I created very simple test: 1 room, i.e. 4 walls. 3D window is empty. About: Sweet Home 3D V4.0, Java 1.6.0_43
Then I tried to create the same in online version, but 3D window is empty too. Home 3D V4.0, Java 1.7.0_21
Then I downloaded SweetHome3DExample5.sh3d and tried to open by my local version. 3D is empty too.