2001 Chevy Lumina no start

Electrical problem
2001 Chevy Lumina 6 cyl Front Wheel Drive Automatic 78k miles

My 2001 lumina has been to the dealer 7 times for a no start situation, I turn the key and nothing happens no noise etc. It has been towed twice but it will usually start after repeated tries. They have fixed ground wires, replaced the battery. Replaced the ignition cylainder twice, and today they are replacing the starter. Last week when it didn't start it showed security on the dash and they changed the ignition(key) cylainder. The keys have also been replaced twice. They also said the wiring was checked. Any ideas?
thanks