2000 Chevy 2500 starting issue

My truck sat for three days and now it won't start. I changed plugs and the truck turns over. Then when I let off the key it kind of gulps like it wants to start. You can hear the fuel pump when I turn the key on. Any help would be appreciated.

my truck sat for three days and now it won't start. I changed plugs and the truck turns over. Then when i let off the key it kind of gulps like it wants to start. You can hear the fuel pump when i turn the key on. Any help would be appreciated.

security light on

Just cause you can hear your fuel pump doesn't mean its pumping up to full pressure. double check your fuel pressure. im sure j cat knows what the specs should be.

what engine? gas or diesel, spark plugs or glow plugs?