If you happen to get an Inbox(1).dbx that means that the original Inbox.dbx file is no longer being used. We can do two (actually a couple of more) different things.
1) We need to isolate this file by moving it to another temporary folder and use DBXtract on it.
http://www.oehelp.com/DBXtract/Default.aspx
A good idea if you have multiple dbx files with the (x) in them already or if you have a lot of message in a single Inbox(1).dbx file. You would move the Inbox.dbx file and anyothers with a lower number to the temporary folder then start DBXtract.
2) If this has just happened and you have only a very few messages in the Inbox(1).dbx file, you can drag them to another folder or out of Outlook Express and close OE, move the Inbox.dbx file to a temporary folder, then delete the Inbox(1).dbx file and restart OE. Once OE has restarted, a new Inbox.dbx file will be created. No (x) added to it. Now, close OE, delete the new Inbox.dbx file, then move the old Inbox.dbx file back to the original folder. Restart OE and your message should be back.