Healing Brush in Photoshop

I have trouble using the Healing Brush Tool in Photoshop. I watch the tutorial, I feel I'm doing what she says but still struggle. I click with the Alt key (Windows) to get the target and sample the surroundings, then I click off the Alt key and just drag across the unwanted object (in this case a wire along the sky) and nothing happens. But, if I then start clicking in the sky, I get plenty of wire marks, lol. Grrr. Any suggestions?