My car starts fine, but within the next 5 seconds, slowly dies. It happened completely out of the blue, it has been working fine until last night when that happened. Im thinking it could be the fuel pump or something.
Has this happened to anyone?

Need more info. Does the engine shake? Any wired noise?
Did you put fuel in?

codes? fuel pump sounds good to me two easy pull tab clip thingies to pull the back seat, listen for it @ key on then cranking/running. then check voltage for same, elictrical computer module thingamajiggies could be making it only power during key-on.