Cook the ground beef and onion into a large skillet over medium heat until browned and crumbly, about 10 minutes. Break the meat apart as it cooks. Drain the excess grease.
Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the macaroni, and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 8 minutes. Drain well in a colander set in the sink.
Add the macaroni to the the beef and onion and place over medium-low heat; stir in the processed cheese until melted, about 3 minutes. Add the salsa, pinto beans, and corn to the mixture; stir and heat until the mixture bubbles slightly, another 5 minutes.