Mac OS X desktop icons may spontaneously rearrange or become unsorted (scrambled) after restarting or force quitting and restarting the Finder. In these cases, items lose their alphabetical or other sorting, and may scatter to various parts of the desktop.
You may be able to resolve this issue by deleting the .DS_Store file on your Desktop. This is a hidden file, but it can be deleted with the utility DS_Store_Cleaner. Alternatively, you can use these instructions to delete the file.