If a user mousesover something—if they place their mouse cursor on it—and nothing happens, then the user will assume that nothing it’s not clickable.
Similarly, if something doesn’t look different when it’s selected, then the user can’t know that it’s been selected. All that is to say: give your users feedback on their actions. Darken the button on mouseover. Highlight things when they’re selected. Show a loading animation if things are loading. You get the idea.