1. Disconnect battery
2. Install new computer
3. Reconnect battery
4. Put emergency brake on to disable daytime running lights (this step is required!)
5. Make sure all doors trunk and hood are closed leave driver window down and reach in threw window
6. Try to start. If it doesn't start, leave the key in the on position for 10 min on 97-03 cars and 15 min for 04 and newer cars. The security light should turn off after this amount of time.
7. Turn off ignition for 3 seconds
8. Try and start the car. It probably won't start. Repeat step 5 two more times.
9. If this doesn't work disconnect battery for 5 seconds and then try and start the car.

If that doesnt work, try this one:

1. Disconnect battery for 10 sec.
2. Reconnect battery
3. Turn key to ON position
4. Do not try to start vehicle, just quickly click to RUN position to engage security light
5. Let vehicle sit with key ON for 35 min.
6. Attempt to crank vehicle. Once vehicle is running, the security light may still be on
7. If security light is still on, turn key to OFF position for 5 sec.
8. Turn key to ON position and security light should turn off
9. Start vehicle and enjoy new PCM