I've owned a 2000 & 2001 Monte Carlo SS. Had the same issue with both. A mechanic friend said it was in the alarm system and to turn the wheel to the left, put foot on break and start without pushing accelerator. Crazy right? But it works, even if you think the battery is dead. Or throw it in neutral and apply the same, turn left, foot on break, not accelerator and turn the key. I did this only after testing the battery and alternator 1st. Both cars start now.