Security light

My car will not start sometimes the security light comes on and it will not start until 12 hr. later. It happens only once a week. I took it to the dealer and they put a new ignition switch but that did not work No one knows why

Wow, that is really weird.

only once a week

If mine did that once a week, I would not call it ONLY. Once every five years, might get an “only” from me.

It’s a longshot, but try replacing the key. You don’t say what year your vehicle is, but GM used to use a system that checked the resistance of the circuit through the key, and wear and/or crud could affect the resistance of the path sufficiently to create intermittant problems.