There is many different things that can be wrong. If you have lights but the starter won't spin, then you could have a bad break light switch,a bad starter switch, bad starter solenoid, or even a bad starter. If the starter does spin but the motor won't start it could be a bad spark plug, bad coil, fuel blockage, carburetor that needs to be cleaned out, or bad stator.
Yes
If you need to jump start the car then the battery may be fully charged but it is defective and needs replacing. A full charged battery will read 12.6 volts at the posts with the engine not running. 12 volts indicates the battery is only 25% charged.
As long as the battery is fully charged it will start no matter the condition of the alternator. Eventually the battery will run down if the alternator is not keeping it charged.
It will start if there is enough charge in the battery to turn the engine over. However if the alternator is weak then the battery will not be charged fully.
Does it turn over? Does it have spark? Does it have fuel?
Fresh fully charged battery and fresh gasoline
Low/bad battery, bad battery connection. If the battery isn't getting fully charged you might not be able to start. If it isn't getting charged, check the alternator.
YOU HAVE TO TURN IT ON Actually, I learned this past week that if it is a gel type battery, you can get a false positive on the battery, so it looks like it is fully charged but actually is not. You can take the battery to your dealer to see if he can charge it or you need a new one.
In most cases a new battery will be charged enough to start the vehicle
It could be a number of things. First check that the battery is fully charged.
The battery will run down and he engine will stop. You will not be able to start the engine. The alternator keeps the battery fully charged.
Be sure the battery is fully charged before you start. A fully charged battery should read 12.68 Volts. If the battery is very low when you check the alternator output it will not give you an accurate reading.
Usually 11.5v is enough to start most cars. A fully charged battery is 12.6v