Unable to use the History Brush Tool to edit a layer after reopening an image.

Opened the myFile.psd file to continue edits from yesterday. All layers are still visible, but when I attempt to use the History Brush Tool to continue editing the layer to paint over the image, nothing happens. It all was working yesterday.

Since I am new to Photoshop I was unsure if there was some default setting that needs to be changed.

This is the trial version of CS4.

The History brush refers to states in the History panel. When you close the file those states are lost.

By default it goes to the first snapshot (top of the History panel).

Ok, I figured it out....

It is not the history brush that I am supposed to use, it is the paint brush. The important part is that I need to ensure to click the white panel within the layer and NOT the picture within the layer. Now, the black removes the layer and the white will add it back.

Originally when the paint brush was select it would only paint white or black but that was due to the image within the layer being selected as opposed to the white box within the layer.

FYI, that's a layer mask.