The commercial pilot reported that during a visual approach for landing at the destination airport, the landing gear position indicator did not indicate that the landing gear was down and locked after it was selected down. The pilot reported he requested a fly by the air traffic control tower, which confirmed the landing gear was extended and cleared the airplane to land. During landing rollout, the landing gear collapsed, and the airplane impacted the runway surface resulting in structural damage to the external longerons on the bottom of the fuselage. During recovery of the airplane, it was noted the landing gear circuit breaker was popped. The circuit breaker was reset, the master switch selected on, and the landing gear was lowered using the landing gear handle. A postaccident functional test of the landing gear using the normal and emergency extension procedures revealed the landing gear extended without incident. The pilot further reported that after maintenance personnel removed the cockpit multifunction displays, he found a piece of screw/nut on the contacts of the landing gear control handle behind the instrument panel, which most-likely created a short-circuit and caused the landing gear circuit breaker to pop. The pilot did not use the airplane's emergency landing gear extension procedure to extend the landing gear during the accident flight.