Fuel Pump?

[The docdoc]

My 1996 Explorer XLT 4.0 liter has started an intermittent problem. A couple times recently when I go to start truck it cranks without starting. Fuel pump or relay possibly? Since I bought the truck two years ago for a hunting vehicle, I noticed when the ignition is turned on half way you can hear a hum from engine that sounds like a pump coming on. I also noticed that when it cranks and does not start, that sound is missing. Any help in trouble shooting is greatly appreciated!
Thanks from a newbie

The docdoc

 

[koda2000]

most likely the fuel pump, but as the pump is the hardest piece to change, it's best to check the relay (swap it with another similar relay) the relay terminals can get dirty/corroded, the inertia switch (although seldom a problem) the wiring going to the pump and the ground.

 

[The docdoc]

Good place to start the trouble shooting, thanks.