Hi - I fixed my car, but the question I want to know the answer to is; what actually makes or causes a car to be flat.dead ? When I say this, I mean when you turn the ignition it just makes an awful drone sound and just won't fire up.

Thanks

You need 3 things to make an engine run.
1) Fuel
2) Spark
3) Compression

When your car doesn't start, it is usually one of these.

In the case of a dead battery, usually the problem is Spark. If the battery is sufficiently flat (because you left your headlights on, your door open, your radio playing etc... ), too much power will be needed to turn the starter motor that there won't be enough to generate a sufficient spark across the spark plugs.

The drone you hear is the starter motor turning the engine, It is waiting for a spark to occur to make the engine power itself, however this is not occurring.

If the spark is okay, check you have fuel and lastly make sure there is no compression problem.