Anti theft light blinking and truck will not start

Hello,

If you have a key fob you can try this:
Hold the panic button on the key fob for 2 seconds. Close all of the doors and while using the key lock and use the key to unlock the lock the driver's door.

Other thing you can try is disconnecting the negative battery cable wait for a minute and reconnect.

https://www.2carpros.com/articles/how-to-reset-a-security-system

Let me know if you have any questions.
Thank you.