Create a Cool Desktop Prank

Want to scare your friends with a cool prank that won't do anything to your computer? Read this article!

Steps

First, find the button on your keyboard that says something along the lines of PRT SCR or Print Screen and press it with all open windows closed and the screen showing your desktop.
Open Microsoft Paint.
Press CTRL and V at the same time to paste your picture onto paint. You should now see a picture of your desktop on paint.
Save the picture in any folder.
Now, close paint and right click anywhere on your desktop.
The first item in the Right Click Menu should be "Arrange Icons By" (In Windows Vista roll your mouse over the "view" option)
Roll your mouse over it and move your mouse down over the words "Show Desktop Icons". This should be checked. Click on it to un check it.
After a few moments, all of the icons on your desktop should be gone. You can retrieve the icons by clicking on the Show Desktop Icons button again to check it.
Right click anywhere on your desktop and move your mouse down to "Properties". (In Windows Vista hit the "Personalize" button.)
At the top of the window that pops up there should be tabs. Click on the "Desktop" Tab. (This would be the Desktop Background option in Windows Vista)
Click "Browse" and find the image of the desktop that you saved. Then double click on it and click on OK.
Now if you try to click on a desktop icon, it will not work.
You can also bring the cursor over the top of the toolbar (at the bottom of the desktop) and drag it down to make the PC completely inaccessible!

Control/Shift and the number "3" to take a screen shot of an open program
Go to the Desktop and open the newly created Picture.PNG file. Default program to open is Preview
Right click on the photo and select "Use Image As Desktop Picture" from menu
You're done!
Finished.

To reset the prank, change the background image back to what the user had originally, drag the toolbar back up and recheck the Show Desktop Icons Button.
If you think the prank will be too light, unplug the keyboard and mouse.

Make sure that whoever you're pulling the prank on has a sense of humor.
If you use the explorer.exe method you can fix it by clicking File-> New task(Run...) and type in explorer or explorer.exe. This eliminates the need to restart your computer