[Submariner409]

Which engine?

During a no-start event narrow the problem down to fuel delivery or ignition - if the engine will briefly fire with a shot of starter fluid into the intake then it has spark but no fuel. If the spark plugs are wet and the engine won't fire at all it's probably an ignition problem.

Have you ever had security system troubles - that can lock out either/or ignition and fuel.

 

[Submariner409]

Sounds like a dead battery. Anything less than 11.8 volts and chances of starting the car are very, very slim.

What does the DIC say for Key: ON voltage and what is the battery voltage when disconnected from everything ?