Nissan sentra sensor for crank shaft position


I was driving my 2004 nissan sentra with 79,000miles at 35 mph when it just quit. After that the engine would turn over but wouldn't start. The mechanics are saying that two crank shaft position sensors are out and need to be replaced. I don't know much about cars and have to take their word for it so I am asking for opinions. Coincidentally, I just had my car in this same shop about a week ago for an oil change and they told me my belts were cracked and needed to be replaced so they replaced two belts. I was thinking they might have knocked something loose?? Thanks in advance for any comments/education/wise cracks.