No electrical power and anti theft light flashing on radio

Hi, my name is Dan.

Sounds like you could have low voltage on the battery. Will the car start if you jump start it? If possible test the battery voltage to see if it's below 12. Generally you require 11.5 volts to get the engine to crank. Are the battery terminals dirty or loose? Once running, checking the alternator charging would be a good first step.
The flashing light on the radio can sometimes mean the battery voltage is low or the wrong key is being used to start it. Do you have a yellow key flashing on the dash when you try to start it? Do the headlamps come on?

I've included a couple links for basic electrical tests for the battery.

https://www.2carpros.com/articles/how-a-car-battery-works
https://www.2carpros.com/articles/how-to-jump-start-car-battery-using-jumper-cables
https://www.2carpros.com/articles/car-battery-dead-overnight
https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked
https://www.2carpros.com/articles/how-to-check-a-car-alternator