if its an auto, check the Inhibit relay. with out this relay, or it not working, the truck wont even try to crank over. the fuel pump will go on, and everything else will work, but it jsut wont crank. there is also an Inhibitor switch on the transmission. that could be gone too. with out both of those things working, the ECU will think the trans is in a gear other than park or neutral. so it wont even crank. just went/going through this myself. except my relay is shorting out and melting/melted a bunch of my wires...