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 ...