97 buick lesabre security light blinking locked out won't start

Have you verified that you are using a properly programmed key for the vehicle? The immobilizer system needs programming for any key you attempt to use. Without this you will not be able to start the vehicle. There is no way to 'relearn' a key without a Tech II diagnostic tool or equivalent.

IF you’re 100% sure that the correct key is being used - turn ignition switch on - does light eventually stop blinking?? Need to know!