you have logged into a different account in you mail setting. Which windows and which internet exllorer are you using please. for email to totally vanish from a inbox is indivudual manual deletion of some sort of infection ?
No guarantee but this may work: Close Outlook Express, click Start > Search and type FOLDERS.DBX (include hidden files in the search, capitals are for clarity only), right click on the file > Delete. If you’re nervous about deleting files then click Rename and type FOLDERS.OLD. Now restart Outlook Express and a new folders.dbx file will be recreated automatically.
If it is not found make sure the search field ‘More Advanced Options’ includes ‘Hidden Files’.
If you cannot access it because it’s ‘read only’, right-click it > Properties and uncheck the Read attribute.