If the car still won't start then get a second person to press the accelerator on the other car, with the gear stick in neutral, while the jumper leads are still attached. Then, while the other car is being revved, try again to start the car.

This works because car engines have generators that recharge the battery while the car is running, and pressing the accelerator will increase the voltage to the dead car.

Also, technically "stalled" refers to the situation that the engine died because you forgot to put your foot on the clutch at the traffic lights (or similar). If the car won't start at all then that means the battery is flat.