For many users, the Windows desktop is a quick and easy way to get to frequently used files and applications. Sometimes, however, Windows will rearrange all of your icons on its own. This can happen if you plug in another display or play a game that changes the display resolution. In some cases, just logging out or restarting the PC could rearrange the icons. There are a couple of things you can do to prevent this from happening in the future, though.
First, right-click on the desktop, and look under "View" to see if "Auto arrange icons" is checked. Unchecking this will allow you to move your icons around at will.