There are a number of possibilities here. A screen shot of the Adjustment settings for the Brush may help. Might want to turn on the "Show Selected Mask Overly" option to see where the adjustment effect should be seen. Are you using a tablet? Pressure sensitivity may be an issue.
Otherwise, you probably just need to reset the preferences. You may also want to test a new catalog.
It was working before the last update. I have attached a screen shot. I did an adjustment brush all over her face, but nothing is happening. I'm on a desktop.
If you want to attach images to a forum post, you have to visit the forum web page, replying to the email will not embed attachments into your post.