Brown beef in a large skillet 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 until al dente, 8 to 10 minutes; drain. Toss cooked shells in butter.

Preheat the 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 the dish from the oven and top with Cheddar cheese, Monterey Jack cheese, and then tortilla chips. Return the dish to the oven to cook for 15 minutes more.

Top with sour cream and serve.