I have Adobe Photoshop Elements 9.
When using it earlier, I discovered that the burn tool would not work, no matter how i adjusted its settings. I also found out that the image was in Greyscale mode, which I manually changed to RGB mode. I hadnt changed it to Greyscale mode so I dont know how it came to be that way. I wonder if there is another mode it needs to be in for the burn tool to work?
Another point, once i changed it to RGB mode, i tried the burn tool on another color and it was working. It will not work on the gray part of the image im working with. Really not sure why that is...
The first thing to try is resetting the tool. Click on the little triangle on the tool's option bar, top left, and reset the tool. That may fix it.
I reset it but still, it does not work.
It seems that the transparency was the problem, somehow.
I saved the file as a JPG and re-opened it in Photoshop, and the burn tool worked.