I'm a Minecraft player, and recently, I was messing around with the f3 key. Typically, I need to press the function key with it, otherwise it would turn up my volume, but after some spamming because I was bored, it was the other way around. I now need to hold down the function key with f3 to turn up my volume. I cannot see what caused this change. It was clearly something to do with the spamming, but I don't know the exact reason or how to solve it. I should note that this also applies to my other f1-12 keys.
I understand the problem is solved but since this could be a common problem, I'm here answering the question. Actually in most keyboards, function keeps are associated with various functions like increasing/decreasing volume or brightness, but by default these functionalities can be accessed while pressing function (fn) key along on the keyboard.
So to go back to previous setting just hold the "Fn" key and press "FnLock" key (here Esc). This will solve the problem.