There have been periodic reports of people having problems with items on the desktop disappearing, particularly on MacBook computers that have been connected to external displays. When this happens, the computer will remain responsive, but the desktop will be blank.
Despite the desktop appearing blank, services for it still appear to be functioning, since invoking the contextual menus for the desktop still work. Additionally, items on the desktop are not missing, since they can be accessed by navigating to the Desktop folder in the Finder.
If this happens to you, a simple workaround is to relaunch the Finder. To do this, press the options-command-escape keys to bring up the force-quit menu, select the Finder, and click the "Relaunch" button. This should refresh the desktop and allow the system to reload items on it.
If the problem continually happens, try some of these suggestions:
Remove Finder preferences
Go to the /username/Library/Preferences/ folder and remove the file "com.apple.Finder.plist" and then either relaunch the finder as mentioned above or logout and log back in.
Remove Desktop's .DS_Store file
Corruption in the Desktop's .DS_Store file may prevent items from being displayed. Go to the Terminal and enter the following command to remove the .DS_Store file on the desktop:
sudo rm ~/Desktop/.DS_Store
Use a program such as OnyX, Maintenance, Cocktail, or (Snow) Leopard Cache Cleaner to remove the system caches, and then restart the computer.
Restart into Safe Mode
Reboot while holding the shift key to run a number of maintenance scripts and clear system caches.
Fix the home folder permissions
If your home folder permissions have been corrupted, you may not be able to access your desktop folder so the Finder will not load items stored in the folder. If this is the case, you can reset the permissions on the home folder by performing the following steps using the Terminal (this should be done when logged into the affected account):
Remove ACLs from your home folder and all subdirectories:
sudo chmod -RN ~
Change ownership of all items in the home folder to your account:
sudo chown -R `id -un` ~
Reset permissions using the OS X installation DVD:
When those commands have been entered, insert your OS X installation DVD and boot off of it by holding the "C" key at startup, select your language, and choose "Reset Password" from the "Utilities" menu. With the boot drive selected, choose your user account, and click the "Reset" button in the "Reset Home Directory Permissions and ACLs" section. After the reset is complete, restart the computer and boot off the main hard drive as usual.