Oldsmobile cutlass supreme security system question.

I have a 1996 oldsmobile cutlass supreme LS 3.1 Liter engine with about 147,000 miles on it. I went on a trip last weekend and when I came back the car wouldn't start. It acts like it is in gear when I go to turn the key over.Absolutley nothing at all happens. it won't engage the starter or anything. I am having a mechanic look at it, but he hasn't worked on cars in 10 years, as he now is an atv/motorcycle mechanic. He seems to think that it is something with the car's security system because the security light stays on when you turn the key and it is supposed to shut off. He has changed out the starter relay and has checked the key and key ignition. He can jump start the car across the starter, but it shuts off as soon as it has burned up the initial fuel, so the starter isn't bad. All of the fuses have been checked also. If anyone has any ideas, I would really appreciate it. Thanks

Greg