this sounds like the key fob is now out of synchronization with the car
Make sure that you don’t press the brake pedal at any time during or before the procedure.
1.Close all doors, then open drivers door and press the Unlock button on driver’s door while it is open, insert key into ignition.
2.Turn ignition from OFF to RUN 8 times within 8 seconds, with the 8th time ending in RUN. Door locks will cycle to confirm programming mode. (if the door locks do not cycle, then it was done incorrectly. You must start over by removing key and beginning from step 1)
(Off is the position where you can remove your key, RUN is the position just shy of starting your car.)
3.Within 10 seconds press any button on the first keyless remote to be programmed. Door locks will cycle to confirm programming. If you only have one remote then skip to step 5.4.Within 10 seconds, press any button on the second keyless remote. Door locks will cycle again to confirm programming. Repeat step 4. for all other remotes.5.Turn ignition to OFF. Locks will again cycle to indicate end of programming mode.
*If this does not work try the procedure with the door closed.
Procedure B:1. Fasten seatbelt and close all doors2. Turn the ignition from OFF to RUN 4 times within 3 seconds.3. Turn the ignition OFF. The system will chime to confirm programming mode.4. Within 10 seconds, press and hold any button on first keyless remote. The system will chime once to confirm programming.5. Within 10 seconds, press and hold any button on second keyless remote. System will chime once to confirm programming.6. Turn ignition to RUN to exit programming mode.
Please note: All steps should be performed in fairly rapid succession. If you never get the initial chime or door lock cycle, that means the vehicle has never entered programming mode. You should remove key from ignition, open and close the door and start over.
OK in that case try the following reset procedure:
I'd try resetting the ECU by disconnecting the battery cables and clamping them together for 10 mins. Remove both battery leads from the battery then use a nut and bolt or G-clamp to hold both battery lead terminals together.
This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default.
This will reset all the systems on the car and you may need the radio security code to get it going again, and ensure that the keys are in your hand when you re-connect the battery as the car may lock and turn on the alarm
in that case I'm afraid that the next step is to get the car to the dealership as only they can then code up a new key and kickstart the security system into life
sorry its not a more DIY answer but this is often the way with security systems