Hello & welcome,
The security light will flash in the instrument cluster to let the driver know that there is a failure in the security system.This does not cut the power to the vehicle off.Check the battery & test it,if bad replace.Check the battery cables for corrosion,if found replace them.Test the alternator for proper charging ,once the engine is started.
Key pad will not lock doors,or open trunk and no clicking sound like a dead battery. No sounds from car at all. Still sound like a battery?