im like 90% certain its the starter. your car doesnt just not start because the alternator suddenly went bad. alternators go bad over time, you start getting diminished power to all of your accessories and its noticable because your alternators working harder and harder to charge the battery, and eventually can't anymore. ive even drove my car with a completely dead alternator in it for 12 miles, bringing the car battery voltage from like 14.something volts all the way down to 8 lol. but ive had my starter go bad before, stopped to get gas, went to turn the car over and it would just click and that was it, had to get towed.