The box is untextured and presumably for bounding box manipulation.
Simply apply a texture to it called 'invisible" in a modelling application and it shouldn't be rendered in PCS2 allowing you to see the rest of the model.
Short of that, if the box does not have a material assigned then you're out of luck if you don't have access to a modelling application.
Well, you could always fiddle with the hierarchy so you can see the inividual pieces by dragging them around in PCS2 until they're visible, but you gotta make sure you don't break anything when you put it back
