Which version of Lightroom are you using?
You could reset Lightroom Preferences, Backup your Lightroom catalog and refer Recover catalog and images after resetting preferences in Lightroom to reset Preferences.
What do you mean that nothing is happening? When you brush on your image you are indicating where you want the adjustment to apply. You also have to slide one or more sliders in the panel (such as Exposure) to indicate what adjustment you want to apply.