This is a PC prank, to make a Windows box appear to be locked up - no response from the Start Bar, no response from the icons on the desktop, nothing. To someone unfamiliar with keyboard shortcuts (more on this later), the PC will appear to be completely locked up. Rebooting will not fix it, either.
While there are a few steps involved, once you have practiced them, you can get it set into place in just the space of a co-worker's walk to the printer & back.
Step 1: Create a Picture of the Desktop & Set It As the Wallpaper
The first thing you must do is to create a wallpaper of the current desktop - this picture includes the current wallpaper image, as well as the start bar, and any and all icons on the desktop. You must close ALL applications, and not be running ANYTHING.
Once you've done that, press the "Print Screen" key. On some keyboards, it is labeled PrtScn or something similar. Pressing that puts an image of the screen in the clipboard. launch Microsoft paint, choose Edit/Paste, and you should now see an image of the entire desktop. Save the image onto the hard drive, then choose File/Set as background (Centered)