Today when tried to start my S4, it didn't. The battery is new and the engine does crank. I checked all the ground connections but it still fails to start. People say that it's the alternator, but the previous owner drives it to Boston everyday and never had a problem. What could it be?

 

Bad alternator would not cause a car not to start.

 

if it cranks, that means its getting power. All the alternator does is generate more battery power. The car could start and run without the alternator before the battery gets drained out. Did you check for fuel? Did you check for spark? If its no on both, check compression. You got to do these before anything else.