2003 impala everything works won't start won'crank

Remove battery terminals and clean both posts and terminals
with sandpaper until you see shiny metal. The black coating is lead sulphate which has a high resistance to current flow both into and out of the battery. Also check the battery in you key as the immobiliser may not be reading it.

you need to replace your switch the theft system is activated with the key maybe try putting the key close to where it goes

you have a shorted battery (have it tested) or there is a loose connection. A starter motor pulls a large amount of current when it engages, a loose conection or shorted battery will all the voltage away from the dash,lights etc.

i would say when the person broke into your car they set off the security system which stops the car from starting, the way to reset the security is to put your key into the ignition turn the key until all the dash lights come on and let them stay on about 15 minutes after the 15 minutes have expired turn the key off and wait about 3 seconds and then your car should start. hope this helps.

Either the chip in the key has failed, or the sensor in the lock cylinder.
You can try a spare key to knock that off the list of possible causes.
Until the PASS module sees the right chip in the key, the car will not crank or start.

Are you saying the engine cranks but won't start, or the engine won't crank ?
If the engine does not crank, you would check for voltage at the starter, the neutral safety switch, and the key switch as well as the ground connections.

You'll have to figure out if it is a fuel or ignition problem.
Is the check engine light on ? Have you checked for trouble codes ?
It could be a relay, the ignition module, coil, fuel pump, or a list of other things.
Could even be a problem with the security system.

Did you check to see if it has a relay..

The alternator is not charging,or the battery wont take a charge.If all accessories work fine when its running after you've boosted it,its likely the battery.
John

Does it crank over normal and just won't start or does it seem to turn over slowly or not at all. If it doesn't crank over like normal, test your battery. Low voltage will do strange things.