3D viewport of SFM Hammer not working

When I open a map in TF2's Hammer editor, the 3D viewport shows the map and all. When I open up the map in SFM's Hammer (I'm using the SFM version because it's the only one so far that I can drop custom files into and have them be loaded) the 3D viewport is pitch black.

What am I doing wrong?

I tried doing that. Whenever I try to change the world model for a static prop, my models never show up in the menu. I've copied them into every part of the custom folder, the tf folder, I learned about VPK archives and put them in one, still nothing.