Unable to paint with a pattern

I am dying out of frustration. Photoshop novice here and I've tried everything under the sun to paint with a pattern. When I was previously editing a photo, I was able to do it numerous times, no problem. But now, I am editing a new photo and not having ANY luck with getting the pattern show up. I've tried the standard method of defining a pattern, new layer, and then using the pattern stamp tool with zero luck. I've tried the "select area" and full with the pattern with no luck. I've watched countless tutorials and read at least 10 relevant guides and nothing has enabled me to paint with a pattern. I have the defined pattern, but I need to actually be able to apply it to the photo and preferably paint with it to control its application. Where am I going so wrong?