Aperture Brushes

I tried to apply a brush aadjustment to my image and the 'brush' did not show up when I clicked on the image. I have done this many times before with no problem, don't know why it does not show up today. I am in the 'enhance section. I put the slider to the setting I want, then I open up the tab next to it to 'brush enhance in' and the dialaog box shows up. In the dialog box for brushes I have brush 'size' adjusted to the size I want, 'strenght' at '1' , the brush icon selected. Hope someone can help me.