not starting

I have a 1998 Chevy Malibu 3.1L V6. Recently it has been starting intermittently. When it starts it works like there is nothing wrong and it can work perfectly for several days in a row. Then all of a sudden I can go to start the car and it just won't start. It will turn over like every is fine...

I rebuilt the engine in my 2000 malibu 3.1L and it ran perfect for about 1 week.... it just shut off on me one day and never wanted to start again. I took it to the Chevy Garage and they told me I needed a new fuel pump, which I already had replaced, but I put a new one just to humor them. Still...