try another key. it may be that simple

Roy

Same thing happened to me two years ago. The wiring harness to the Security ignition system runs underneath your steering column cover.,the one that covers your turn signal switch and wiper control.Any way, remove the cover( 2 screws on bottom) and check the wires CAREFULLY( make sure you don't miss any wires.) to check for cracked insulation. It seems that if you use your steering wheel adjustment system,moving the steering wheel up and down when you exit the vehicle., the wires( which are very tight under your steering column) get frayed and ground out to the metal frame shorting your Security System which won't allow your key to start the vehicle.. My mechanic found breaks in my wires, taped up the harness with electrical tape and I have had no starting problems since. Sure hope this solves your problem. It was very frustrating to go through this and my mechanic actually found it accidentally