Importing Models

I am for some reason unable to get any mdx files to load when I import them I have followed multiple training things from the forums aready but still i can not get the models to load. I am importanting them and I am change the directories to custom ones depending on the the folders and I am able to get the blps to load up that i am importing but I cant get the models to load. Any help would be awsome cause I am in the process of making a new map that i think all can enjoy