Twenty minutes of radio time or a few minutes of headlight operation on a non-running engine should not run down a good battery.
Question though. You state it was fine and then nothing. By that do you mean there was absolutely no click sound, slow starter motor operation, etc?
If this car has an automatic transmission maybe there’s a fault with the neutral safety switch; sometimes called a range selector switch.
This is the device that prevents an engine from being started in anything other than PARK or NEUTRAL.