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the button moves but it doesn't work
the button can moved but brush tip won't sharpen
Sorry, I was mistaken.
What is the Control setting – »Pen Pressure«?
The triangle with the exclamation point next to it seems to indicate that there is a problem with the feature, maybe your tablet or its driver don’t meet Photoshop’s Requirements.
Go with @c.pfaffenbichler 's suggestion.
If that does not work for you, try resetting the tool.
Here's how. http://www.dreevoo.com/content.php?id=2312