Hi, I am Dave, I will help you with this.
The Actions associated to the Function keys (F1 - F12) are controlled by the PC manufacturer or the keyboard manufacturer, not by Windows, because the actions for those keys vary from PC to PC.
1
If there is an Fn key on your keyboard, try pressing Fn + Esc to reset the function lock on your keyboard.
2
If not, do you have any specific drivers or software installed for your keyboard?
What is the make and model of your keyboard?