Security light Problems
There are two little white wires (with contacts) in the column. When you turn the key, it creates a complete circuit, the PCM reads the resistance in your key, makes sure it is correct and lets the car start. If these contacts are bad, the resistance is read incorrectly and the car won't start.
Before you start snipping wires, if you have a spare key, try that first. Also, clean the chip on your key and the key tumblers in the column with a little alcohol and see if that works.
If that doesn't work, do a search on VATS and see if you can find posts regarding disabling it. If you still need help, shoot me an email.

