Fbx files won't load?

I try to import fbx files from a disk drive into my unity project and the fbx will simply remain in import loading mode indefinitely. However, if I close my Unity project and reopen it, the fbx is now present in my assets folder, but I am forbidden from dragging it onto the scene to display it. What could be going on here?

Files must be massive!
Try and just drag one Fbx file in and see what happens.