Anti-theft system reset?

That car should have a passlock system. The key cylinder has a magnet that is picked up by the sensor that is part of the ignition cylinder housing. Changing the key cylinder alone shouldn't need to be re-flashed. However it does need to be re-learned using a specific procedure.

Start with the ignition in the OFF position
Try to start the engine.
It should crank but not start, and the security light will be flashing.
Release the key to the RUN position and leave it there for 10 minutes.
Turn the key to the OFF position for 20 seconds
Try to start the engine again. If it starts and runs, everything worked!

If the engine still won't start, repeat the above steps 2 more times (30 minutes total)

If this doesn't work then you will need to have a scan tool connected to determine if the problem is in the security system or if it's something else.