The up and down buttons don't work.

Hello everyone, I have a small problem. My up and down keys (the arrow keys) don't work. When I try to press them, it doesn't scroll down the page completely, but it jumps to headings, etc. (like on YouTube, it brings up the search bar). And I don't know how to fix it because it only works if I hold down the "fn" key at the same time. If you know how to fix it, please let me know, thank you.