When I turn the key it doesn't start?

Engine Performance problem
2005 Chevy Uplander 6 cyl Front Wheel Drive Automatic

Sometimes when I go to start the vehicle, I let go of the key and the vehicle still tries to start by itself and then it go woof and stalls. It never got to start. This has happened periodicly since I have bought it in 2005 brand new. The chevy dealer said he can only pinpoint the problem when it does it. Well. It never did it repeatedly to where I could take it in to the dealer. It was randomly occurring. Well, it is now doing it more frequencely with more of a vengence, but, still at random. I don't want to be in the middle of the new jersey pinelands when it finally breaks down all together. Can you help?

Van wont start, it just clicks still have power to lights and stuff just wont start.