How did you check it? Did you check continuity with a multimeter?
Sometimes it is not the switch but the soldering joint to the PCB that has broken — and that is often fixed by reflowing the joint by heating it with a soldering iron, and perhaps adding a little extra solder if needed.
And BTW, do also check that there isn't a DIP switch (or key-combo equivalent) that your brother could have fiddled with, which could have disabled that which you would usually use the Fn key for.
