First, scan your HDD to check for and correct data corruption. If you have multiple partitions, you will need to scan all of them. Usually, the problematic one is your boot drive. You may need to schedule a drive check and reboot your computer. Usually, it's just some soft error. After the correction, your Outlook Express should load properly.
If you carefully follow these instructions, you may be able to recover them, if not, then your .dbx file can be severely corrupted and you need to see next powerful instrument created for such issues https://www.repairtoolbox.com/outlookexpressrepair.html Outlook Express Repair Toolbox Additional useful tips about MS Outlook Express dbx files you may read and learn below https://itknowledgeexchange.techtarget.com/itanswers/after-compression-the-letters-disappeared-in-the-outlook-express/ https://knowledgemanagement.ittoolbox.com/groups/technical-functional/km-general-l/i-lost-all-the-letters-there-is-no-backup-5614281 Follow the below given points to create a backup with outlook repair tool, & resolve the issue: Go to the Microsoft Support website and search for the MS06-076 update. Download the file & install it on your computer. The action will help you to build a backup of the .dbx file whenever you compress the database. Close the Outlook Express program, if running. Go to the desktop screen on your computer, and open “Recycle Bin.” You can find the .dbx file, named as inbox.dbx in the “Recycle Bin.” Right-click on the file and click on “Restore” from the resulting menu. Start “Computer” if you are running on Windows Vista or “My Computer” if you are using Windows XP. Go to the “Tools” menu and select “Folder Options.” Open the “View” tab and check the bubble against “Show hidden files and folders.” Go to the Outlook Express program and select “Options.” Click on the “Tools” option. Go to the “Maintenance” section & select “Store Folder.” Note down the location of the Store Folder and close Outlook Express. Navigate to the Store Folder location noted, and check if there are any .dbx files in the directory. Make sure that you do not alter any .dbx files as clicking on the files may damage them. Create a new folder in the desktop, and move the corrupt .dbx file into it. Copy the backup of your .dbx file in the original directory. Delete the folder created on the desktop with corrupted .dbx files transferred to it, & resolve the issue. You can search online for a third-party .dbx Outlook repair tools, if MS06-076 update does not automatically creates a backup of your .dbx file. Go through the instructions carefully for the third-party .dbx recovery tool and fix the corrupted .dbx file gsystem. So, if you want to bring it back onto the desktop, simply mark on the check box, which you had earlier removed, against the “Windows gadget platform” in the previous steps.
