Q: Nissan exterra security light flashing car won't start

This suggests you have a malfunction in your security system that is disabling the ability of the vehicle to start. When the security system is functioning properly, the goal is for it to disable the car’s ability to start when the system detects that the vehicle may be compromised. There are a series of vehicle sensors that detect this and when these fail, this may cause the security system to inadvertently trigger the security system. I would suggest having the vehicle towed to the nearest Nissan dealer to have this reset or replaced.