Car won't start

I have a 2000 chevy malibu 3.1L with 89,000 miles on it. My serpentine belt broke a couple weeks ago, had it replaced. 3 days later I hear a low knocking sound only when driving and then my check engine light came on. I took it to a mechanic and he couldn't find anything wrong. 2 days later I drove home, parked the car and 15 min later went to start it and it won't start. The engine tries to turn over but nothing. I can't hear the fuel pump priming the engine. I'm hoping it's not the fuel pump, I would like to have other issues checked before someone drops the tank and replaces the pump. Thank you for any info regarding this matter.