Does you security light stay on all the time, or flash?
If it flashes at start up, see if it stops then try and start teh car.
This has to do with the passlock security system and when it craps out, you usually get stranded somewhere
But you never said what year and engine size,
so its hard to say.
BTW These are two very important things needed in properly identifying troubles.
And every other person forgets them

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