You may not be trning the key hard enough, like my cabbie, they seem to all have the same problems eventually. It sounds like a bad idea, and don't do so in an angry way, but make sure to twist your hand hard, and strong when you go to start her. Be sure you're pressing the brake what you're starting her, and twist HARD.
Do you have dash lights? Everything else powers up?
Can you verify your car is in Park or Neutral? Move the shifter around with your foot on the brake while cranking - does that help at all?
A few things could be happening.
Your battery could be dead. It may need charged or replaced. Will your car take a jump from another car?
You could have a faulty starter, drawing too much current.
You could have a fautly starter relay or starter solenoid.
You could have loose battery cables, or excessive corrosion that needs to be cleaned.
You could have a loose starter signal wire from the solenoid, which may also be corroded.
You could have a faulty TR (transmission range) sensor that tells when you are in park or neutral.