No. The engine starts the car.
No. But you may be out of gas and not know it.
Yes, one bad cell in a car battery will cause the car not to start.
Unless your car is a diesel, they can certainly keep your car from starting if they're missing. They can also become fouled or badly worn, which, again, could keep your car from starting.
No, not if the battery is fully charged.
It really depends on how the alarm is wired into the car. If it is wired into the ignition system the yes it will keep the car from starting if triggered.
No.
Yes it can
Tehe timing belt and dozens of other things can keep the car from starting.
It can.
Yes
It depends on how bad the leak is .If its a really bad leak to the point where the car is starting to overheat then no