Pontiac

Saw this in another forum and thought it could help you. You might need to have the passkey III system relearn your key. Do this by 1. Turn the key to the on position but do not crank it over. Your Security light should stay lit. 2. Leave in the on position for 10 minutes or until the security light turns off. Do not try starting the car. 3. Once the security light turns off, Turn the key off for 5 seconds. 4. After 5 seconds, try to start the car. If this doesn't solve the problem, repeat steps 1-3 3 more times, a total of 30 minutes, and then try to start the car again. Hope it works for you.

I'm having a similar issue and tried this but to no avail, I have been told by various mechanics that the dealer may have to reprogram the ecm.