Cranks but no start

The car battery had gotten low, so I jump started it. Engine started fine, but when I got out to take off cables it started sputtering and cut off. Have not been able to start it since. Engine cranks fine. I noticed at first I could hear the fuel pump priming when I turned ignition switch on, but now there is no priming sound. Also noticed that fuel gauge does not register, and the low fuel symbol is on longer than the initial dash lights on check. There is a half tank of gas. I swapped out the fuel relay, it looked fine. Also checked fuses and they are good. What else can I check, and in what order? The car was just running well before this happened.