Security light stays on in your 1998 buick lesabre and the car sometimes doesn't start any help?

The first vehicle anti theft system was installed in the 1985 Corvette. You can read a very good article about the PasskeyIII and Passlock systems that were introduced in 1998 in www.motorage.com June 2005 P.28-33 "Communication Breakdown". Until then just sit in your car and wait about five minutes until the system resets.