'03 chevy silverado v6 vortex wont start?

[glisten1975]

Truck was running fine and then after a week and a half of not driving it, it wont start. (Battery and fuel pump is fine, bought new spark plugs.) The motor will turn over but wont start up. I'm getting spark. The cylinders load up with fuel and create back pressure. During the week I didn't drive it, we had a cold spell and alot of rain.

Does anyone know what might be causing this problem.