Having issues with Magic Wand Tool in CS4

[drgrafix]

OK, I'm a senior but I'm usually smarter than this LOL. Anyway, I'm having some flaky issues with the magic wand tool in PS CS4 on my mac. Been great for well over a year, but all of a sudden I'm having problems isolating any areas in image files, and I'm even talking about strong difference ones like text on a sky background. I go to use the magic wand to capture the text (like a logo), and no matter what my settings are numerically... it just selects the whole picture. Could I have possibly tripped some preference setting that is obscure?

Tell me what I need to do to fix this. And of course... thanks in advance for any/all help on this!

[RTW1]

The magic wand tool is linked with the colour sampler tool if the colour sampler is set at too high a pixel radius you would never be able to select just the text, see images. Also do not have the threshold setting any higher than 40 at the most.

[Albacore]

Not so sure that I would agree with the last member who replied above most of my samples that I have to deal with are of poor quality and I have the threshold setting normally around the 80 mark so that I dont loose a good part of the image edge detail. Can't think of any settings that would really stop it working can you use the Lasso Tool instead? does it work!

[RTW1]

The sample size set with the Eyedropper tool has a direct link with the magic wand tool. Image No1 shows the gray text unselected. Image No2 shows the selected text in green with the Eyedropper tool set to sample a 3by3 pixel then magic wand clicked on the gray text, as you can see it has selected just what was wanted. Image No3 first the Eyedropper tool was set to sample a 31by31 pixels, then I sampled again with the magic wand tool and as you can see by the green showing the sampled area it is a failure.
I hope anyone thats have strange problems with the magic wand in Photoshop checks out that the Eyedropper tool is not set at too big a radius.