Problems with my Chevrolet cavalier

Good afternoon to all users of this page. I'm writing because I have a problem with my Cavalier... I lost the keys once and changed the ignition switch. The old keys didn't have a chip or anything, and neither did the new ones. The car ran fine for a couple of months, then it stalled and wouldn't start again... and a red light with a padlock symbol is on the dashboard. What can I do?

THANK YOU FOR YOUR HELP...

The Cavalier doesn't use a chip in the key, but it does have a sensor in the cylinder that needs to be programmed when it's replaced.
You didn't mention if the Theft System light on the dashboard is solid or flashing. If it's flashing, you need to program it.
Several forums suggest different methods, but the most common is the following:

Try to start the engine (it won't start) and then leave the key in the "on" position; don't turn it to "off".
Wait 10 minutes for the light to stop flashing; it will stay on.
Wait another 10 minutes with the light on until it turns off.
Turn the key to the "on" position.
Wait 30 seconds.
Start the vehicle.

Thanks friend, it worked for me

earfidel, could you post this in the known mechanical failures section so I can archive it for when this same problem comes up again? That way it's easier for them to find the solution if no one answers. Thanks in advance.

Always at your service. I've already uploaded it to the Known Mechanical Problems section.