Tacos in Pasta Shells

In a large skillet, brown beef over medium heat until no longer pink; drain. Add cream cheese, salt and chili powder; mix and simmer for 5 minutes.
Meanwhile, bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain. Toss cooked shells in butter.
Preheat oven to 350 degrees F (175 degrees C).
Fill shells with beef mixture and arrange in a 9x13 inch baking dish; pour taco sauce over shells. Cover with foil and bake in preheated oven for 15 minutes.
Remove dish from oven and top with Cheddar cheese, Monterey Jack cheese and tortilla chips; return dish to oven to cook for 15 minutes more.
Top with sour cream and onions; serve.