I do not understand what you are saying.
I understand that there are keys that need the Fn key to be pressed to do a different function. For example, the up arrow key, which moves the cursor up when it is pressed, when the Fn key is also pressed the up arrow key moves up a page (Page Up).
So are you saying that it works when the Fn key is pressed (and so the up arrow key causes PageUp) but when the Fn key is not pressed, the up arrow key is still doing the PageUp thing? If so, I would suspect a stuck or broken Fn key. Maybe disassembling it, cleaning it, and reassembling it would fix it. If not, you may need to replace the keyboard.