Why won't a 2002 Focus turn over?

1.Check for corrosion on the battey terminals. 2. check fusible links and cable to starter for damage and tightness. 3.If a manual transmission the clutch must be engaged. 4.If automatic transmission try starting in neutral. More info needed: does the door open buzzer or headlight buzzer work when door is open. If not then there is a battery problem. Has the car been in an accident? There is a breaker for the fuel pump that trips when bumped from impact.

2. When the timing belt broke in my car, there was a focus safety system that would not let the car turn over until that was fixed. That way the piston wont slap valve.