I had a flat battery, took it of to recharge it, when i put it back on the car would not start. When you turn the ignition, the dash board lights stay on & there is absolutely no sound from the starter motor. Put a new starter on yesterday, still nothing. Could this be an ignition barrel fault, ignition switch fault or has the immobiliser kicked in?

Economy mode usually comes on when the computer senses a low charge on the battery and conserves power to start the vehicle.
1. If you can start the car by jump starting from another vehicle with its engine running then you know your battery is the problem. In some cases when you completely drain a battery you have issues with them ever after until they fail completely.

2. If you cannot jump start from another vehicle then turn everything off and disconnect the negative and then the positive lead on the battery terminals and leave it for 10 minutes. Then connect it back up again (positive lead first and then negative lead last) and put the key in the ignition and turn on the ignition but do not start the car. Leave it there for 5 minutes and then turn the ignition it off. Then try starting again.

3. You have not mentioned if there are any other warning lights being displayed on the dash which you have not mentioned in your question. Please check this carefully because it is also relevant to this problem if there are other warning lights displayed.

I had this same problem with my 2004 gmc envoy. Mine was a key problem. I had a 2001 impala that had identical keys that contain a chip that is read by the ignition switch. Both of my keys were near each other on the keyring and when the impala key was to close to the ignition the truck would not start and the light came on that looks like a lock. I took the impala key off the keychain and never had another problem.

Will it crank in neutral ? Do you have power at the starter post ?

When the alarm sounds, turn the key to the RUN (NOT START) position, then OFF - do this 10 times rapidly.
Many alarms will turn off and allow the car to start with this method.

the key lost synchronization with the the computer. its a common problem with these new high security systems they're very sensitive. this made the battery die, next step is to take the car to the dealer, dont try to start the car anymore. if you have any questions call Priority Automotive Locksmith 866 999 7858

you should check the starter and wire.

Sounds like just a flat battery to me.?
Booster-start should get it going, or take the battery out & get it recharged.?
Best of luck

when starting the car the starter motor uses a huge amount of current

normal things like lights radio ac dont use that much

most of the time the radio will work but the car will not start

i recomend recharging the battery before you start replacing anything

i amagine that changing the barrel would not be that hard
the hardest bit would be finding a barrel and keys

did u have the alternator tested to see output get a jump if the car starts takeit to a auto zone have him test the battery and alternator for free

try checking the main relay under the dash