slider does not work to change icons size.

I just bought a mac pro 10.8.3 and I wanted to change the size of the desktop icons size. I went to Finder, view, show view options, and then moved the slider to a bigger size but no change whatsoever on the icons.Itried also arrange none etc , but the icons do not change. I was sure I was in the desktop window and the sliders moves but nothing happens. Any suggestion? Thanks