select all HELP!

okay I am so sorry to post something this trivial, but I have been trying to figure this out on my own for the past few days and it's starting to drive me nuts!...

for some reason unknown to me, every time I click on the select box then select what I want, after I let go of dragging, the selected area, or "marching ants" go from being a rectangle or square with sharp edges, so a shape with curved corners and I cannot figure out how to get that to stop.

does this make sense? or more importantly, does anyone know how to stop the marching ants from marching in curved lines? any help is much appreciated.

happy photoshopping to you all!