No start. Not getting fuel. Pump, Filter,or ?????

when you turn key to on,not start.can you hear the fuel pump prime(humm)for 2 seconds.you can get a helper to help do this.open gas cap,listen close,while someone turns key to on.every time key is turned to on,the fuel pump primes for 2 seconds,then turns off.then when cranking the truck,when the engine computer see's rpm,the pump starts and runs untill you turn engine off again.