So the motor is turning over, but the car is not starting?

If the starter seams strong, do the usual things like check spark etc. You've definately got enough voltage for it to start. May pay to load test the battery too, if you don't have a load tester leave your headlights on for about 5 mins and if the battery is drained massively it is probably time for a new one.

Check your earths also and battery terminals are tight