The mod key is set to left alt and when I hit f12 with no other keys, it turns on and off aerodynamic forces overlay, I'm not using a laptop so there isn't an FN key, so I don't think it's in the media mode. On my keyboard it says f12 is also scroll lock, I'm not sure if that has something to do with it. All the other function keys work as well. I have a laptop that also has ksp and the debug menu works fine on it, so maybe something is wrong with the install?