My 1999 Olds Cutlass wont start

I was about to head home from a friends and started me car to let the ac
come on and cool the car down. I started the car and went back inside and
then came back out a few minutes later to leave, when i came outside i could
hear the car running but it was running a little rough so i was going to get n
and rev it up a little but before i could get to the car it shut off. i wasnt worried
because it has done it before and normally it would start right back up.
Except this time, now all it does is crank and crank. I changed the fuel pump
relay that didnt work so i changed the fuel pump and fuel filter i have plenty
of fuel pressure. i have spark in all cylinders. what could be the problem???
Help quickly it is the only vehicle i have right now