Restoring default settings without losing files

[OlandExport]

So my son was playing with the macbook while I wasn't watching and I have no idea what he did in the few seconds that he had it.
Now everything action I perform on the macBook is sung back to me as the funeral march, which surprisingly got old very quickly.
Also many of the function buttons stopped working or perform different tasks that they once did. i.e decrease volume now minimizes everything.

So I just want the old settings, or default settings back without losing my fies.

Thanks