My 2001 5.9 did the same thing, it was the pump. I figured it out by cranking it and pouring a small amount of gas down the fuel injector. It gave a very brief attempt at starting (just a sputter). So I knew that the electronics were functioning. There is a fuel pump relay that can prevent currant from getting to the plugs that can also cause that problem.
You can accomplish the same thing with a lot less hassle by squirting some starter fluid directly into the air intake. If it starts, then look to the pump as the issue.
Crank and/or cam sensors may also be the cause.
