Sometimes, for reasons I'm not sure (amount of polygons comes to mind) an object's display becomes a box instead of an outline of what that object is.  Now I know you can choose what kind of preview mode you want, but this seems to happen on its own from time to time (and again, I assume it's because of polygon size, or something)....

The model I'm working on was made in Silo....it's a tree with roots flowing over a terrain, and I would like to be able to populate the ecosystem with better precision (between the roots, etc.) but because the tree and its roots have become a box in the preview I can't see anything.  Does anyone know a way to fix this so that I can see the basic outline of the model again....

Thanks!