The article [Q313055] states that Outlook Express mail folders, e-mail messages, and Address Book are missing after you upgrade and occurs because the Windows XP file structure is different and the files for Outlook Express are no longer in the same location and this same anomaly can be experienced as explained in the article [Q295965] which states that when OE is started, some existing folders (Inbox, Drafts, and so on) or personal subfolders may be missing and can be caused if the file "Folders.dbx" (the Indexer) is damaged or corrupt. To resolve this issue, rename or simply delete the Folders.dbx file for the impacted identity, and then start OE which rebuilds it. Please be advised that this same anomaly may occur if this file for certain other folders is also either damaged or corrupted. This Knowledge Base article also provides a step-by-step procedure to help you find your previous mail, folders, and Address Book, and import them back into Outlook Express.
CAVEAT: The Folders.dbx file however keeps track of Active News Group Subscriptions too. Should this be important to you, do not delete it. If you do, that information will be lost. Again be advised, the file Folders.dbx is the file which categorizes and maintains the default mail Store, the user created OE folders, and default OE files. If a certain file or folder is moved or copied into the Mail Store inlieu of using the correct Import method, the Folders.dbx would not be aware of this change and therefore consider the replaced ?.dbx file or folder as corrupted. To make sure things are in sync if copying or moving either into the mail Store, delete the Folders.dbx file before starting OE to ensure that a new and accurate one is created. Even afterwards, perhaps simply deleting it and opening OE will fix you right up. Should the system have asked, "Overwrite . . ."? when a copy or move was performed, anything previously at that point was lost.