I am a fairly recent user of CS5. I find it brilliant. However, I have encountered a problem, no doubt of my own making, with accessing Curves. By whatever route I use I get a panel with restricted facilities. For example, there are no sliders for establishing white point. When I hover over the Target Adjustment Tool button I get a "No Entry" sign. What stupid thing am I doing/not doing? Any advice would be really appreciated.
Can you post a screen shot of the curves pallet? I know your cursor will not show, but also show your layer pallet so we can see what sort of layers you're trying to adjust. There are no sliders for white point with curves. You do that by adjusting the ends of the curves or by using the eye droppers.