A. Data can disappear from the All Users folder if you've performed an in-place upgrade of XP (i.e., installed XP over an existing XP installation), used the XP installation CD-ROM and selected R to repair the XP installation, or upgraded XP Home Edition to XP Professional Edition. To recover the missing data, you must restore the information from a backup copy.
To prevent this problem from happening in the future, look for and delete a file named undo_guimode.txt. This file is typically in the \%windir%\system32 folder. The undo_guimode.txt file often appears on systems in which the manufacturer has preinstalled XP. The first time you start such a system, the system often calls a wizard that creates the file.