First enter layout mode and select layout setup....
Make a note of the text shown in "show records from". This is the name of a table occurrence found in Manage | database | Relationships. Then dismiss this dialog and double click one of your fields that displays Missing to bring up the specify fields dialog. Note the text in the drop down in the top of this dialog. This is also the name of a table occurrence in your system. In simple layouts, the two names match, but it is also possible that you add fields from a table occurrence that is linked to the table occurrence specified in layout setup...
If you have a portal on your layout, it refers to a related table occcurrence in portal setup | Show related records from. This portal then is like a small layout based on the portal's table occurrence. Fields in side the portal thus follow the same pattern, they should refer to either the table occurrence specified for the portal or an occurrence that is related to it.
You'll need to compare these settings to the relationships tab in Manage | Database to figure out what happened and how to correct it. Odds are that either a table occurrence or a relationship line was deleted from this tab and this "broke" your layout. The other possibility I can think of is if you changed the table occurrence in Layout Setup | Show records from and failed to update the fields to come from the new occurrence or one related to it.
Have a look at the upload image, which show the manage l database. There is only 1 table in the file which is straight forward, but somehow i don't know what went wrong. the details show 0 fields /13196 records.
What do you see on the fields tab?
It appears that all field definitions (and their data) have been deleted.
Hope You have a back up copy of your database as this is not something that you can undo.