Burn tool

The burn tool does not work well for this purpose. For example, if you have a picture of someone with blond hair, the tool fails if you wish to make the hair red. In order to accomplish this, I would make a selection of the hair, place the "hair" on a separate layer, open a hue/saturation adjustment layer above the "hair" layer & link these 2 layers (press CTRL+ G). In the dialog that opens, click the "colorize" box, and work the sliders.

Feel free to post your picture so that we may provide targeted guidance.

What OS and version of Elements are you using?

Can you show us a screenshot of what is happening and include the tool options panel settings.

All I can suggest with the limited information you have provided is to reset the Tool through the controls that appear on the right side ot the Tool Options panel. 

And if that doesn't work, tryresetting the preferences file. Go to the Edit>Preferences>General tab and click the Reset Preferences on next launch button.