Do they still show up if you navigate to the "desktop" folder of your computer? In Windows Explorer, this will either be in "C:\Documents and Settings\USERNAME\desktop" (for XP) or "C:\Users\USERNAME\desktop" (for Vista). If they show up here but not on the desktop, perhaps they somehow got caught off the screen. I've had it happen to me before, when I increased the icon size too much. Try pressing CTRL+A to select all icons, then drag the icons around the desktop to bring the missing ones back on the screen. It's kinda hard to describe this, so I apologize if it isn't very clear.