Car turns over but will not start

I initially had a bad alternator and I change the alternator and the battery and now a new starter. It would start run for a few seconds install. I checked the security system and it is not showing that it was triggered no signs. I moved on and changed out spark plug spark plug wires yesterday and the car again would start and stall a few seconds later. So after and doing some research I changed out the crankshaft sensor and the camshaft sensors today and I yet no start. It will turn over, I can hear the fuel pump run for about five seconds. I get fuel at the fuel rail but I'm not sure why yesterday I got it to start stalled out and was difficult to restart. But I got it to restart two or three more times. I just couldn't keep it running. Now today it will just turn over but not start. Can you please help?