I just stupidly dragged 'Macintosh HD' out of the Devices column in the finder. I tried to drag it onto the desktop to get a Macintosh HD icon on my desktop, but instead it did the "poof" thing and now I have no Macintosh HD icon at all. How do I undo this?
To get it on the Desktop, click the desktop, view from the apple bar. View Options and add it to the desktop. In the Finder window you can do the same. It should be located under preferences.