Samsung NV75J3140BB oven - no reaction; the letter L on the display

Good morning,

I have a Samsung NV75J3140BB built-in oven. He hasn't caused any trouble so far. Today I used it as I always do. After taking the food out of it, the letter L appeared on the display. The display does not react to anything. The oven does not start. Turning the knob to select the program turns on the light inside the oven, but it does not work.

I found nothing in the manual about such an event.
What could it be? What should I do?

Thank you for your help.

Hello. The letter L is an attached parental lock.
Press the clock and the hourglass simultaneously for 3 seconds.

Thank you!
Thinking does not hurt.