Please help - Photoshop eyedropper won't change color in color wheel

Hey!

I hope any of you guys can help me.

When I try to pick a color with the eyedropper it won't change the color in the color wheel anymore.

The eyedropper is definetally working though, because the color in the little foreground color square is changing, when I'm using the eyedropper tool.

Only the color in the color wheel / color cube/ RGB Sliders/ ... stay the same. 

Thank you so much! Getting more and more frustrated, because I cant continue working 😞