Here is simple computer prank you can play on your friends.
Instructions:
#1. Take a screen shot by pressing the keyboard’s [PrtScr] button.
#2. Open up Microsoft Paint.
#3. Paste the captured image into Microsoft Paint by pressing [Ctrl] and “V” (or choosing “Edit” from the File menu, then selecting “Paste”). The screen shot will appear.
#4. Select “Image” and Rotate by 180 degrees.
#5. Save the picture. Be sure to remember where you saved it.
#6. Close Microsoft Paint.
#7. Right-click the desktop background and select “Properties”, then click on the “Desktop” tab.
#8. Click the “Browse” button on the right of the window.
#9. Choose the picture that you saved from Microsoft Paint.
#10. Click “Ok” to save your changes.
#11. Right-click on the desktop background and select “Arrange Icons By”, then select “Show Desktop Items” to uncheck it. It may take a moment for the effects to be made. If your friend’s computer doesn’t show the “Show Desktop Items” option, you may move all of their desktop icons (user created ones, not the Recycle Bin, etc.) to a different folder. You may also hide desktop icons such as “My Documents”, “My Computer”, “Internet Explorer”, etc. by right-clicking on the desktop, selecting “Properties”, clicking on the “Desktop” tab, and then clicking on the “Customize Desktop…” button.
#12. Close all open windows.