marquee tool problems

I am using Photoshop CS on my powerbook G4, OS X, jaguar. all of the sudden, when I try to use the regular, rectangular marquee tool, it makes the selection with rounded corners-a rounded marquee tool. No matter what I do, in most of my images, this happens. in several files, the tool will behave properly, but in most it will not. It doesn't matter which format the image is in, or when it was created.
I even tried re-installing the application, but this did not correct the problem. please help!!!

With Rectangular Marquee Tool selected (first tool, top of left column in the Tool Box) look up to the Options bar. Make sure the value in the "Feather" numerical entry field is set to "0" px.

Now, please consult your Photoshop Help files or manual and do a search for "Feather" so you can gain a better understanding of what's happening with this particular occurance.

Rounded corners indicate that you have a feathered selection. Check your Feather setting in the Marquee options.

Carl.

I should re-read the thread before hitting 'Post Message.'