Photoshop: Color picker is using system color picker instead of the Adobe Color Picker

When I use the eyedropper tool to get a hex number it lunches the basic color palette, no hex numbers, not color picker.
But sometimes by magic it does lunch the color picker.
Is this a bug in CS5.1?
I'm using Windows 7 PC - Intel(R) Xeon(R) CPU E31225 @ 3.10GHz.

I get this:


I want this:


Thank you for your help and best regards.
Elena Pascual