A problem with my eyedropper tool...

For the last two weeks or so my eyedropper doesn't pick up the correct colors.  Any color I try to pick up it always picks up the darkest color near the one I want, even zoomed in it does this.

If it were any other tool, I'd live with it...but I use my eyedropper all the time...does anyone have any idea what has caused this and how I can fix it?  I use PS CS3

Thanks for the help :)