First level

Today I designed and created the first level for the game.  Here is a quick fly around of the level, though it is shrunken from what it is going to end up being:

I have some models that I found online and have loaded into the game engine that I want to spread throughout the level, however I have come across a problem.  If I attach any of these models to the root node, I get a black screen in the game.  I have tried scaling and moving the models away from the camera to make sure it is not an issue with the camera being inside the object, but that is not it.  Here is a video showing the bug I have:

Hopefully this problem will not take much longer to figure out, and some time away from it will make the solution more obvious to me.