In the relationships window, click the Show All button (toolbar), just to be
sure there really is a problem.
If the relations still don't show up, the database is partially corrupt, and
Name AutoCorrect is the likely culprit. Uncheck the boxes under:
Tools | Options | General | Name AutoCorrect
Then compact the database:
Tools | Database Utilities
Now we need to recreate the database, so you can rebuild your relations:
1. Create a new (blank) database.
2. In the new database, turn off Name AutoCorrect
3. Import everything from the problem database:
File | Get External | Import
Under the options button, uncheck the Relations button, so you do not import
the problem relations.
4. Build the relations again in the new database.
It would also be worth checking that you have the latest service pack for
your version of Office, and (most importantly) for JET 4. You can download
both from the Downloads section at:
http://support.microsoft.com.
For more information on the problems caused by Name AutoCorrect, see:
http://allenbrowne.com/bug-03.html