How to reset the menu items to defaults
Inside the CiviCRM root directory is a "sql" folder, and inside that is "civicrm_navigation.mysql".  Copy it to "civicrm_navigation_restore.sql" and edit the copy to remove all of the SQL commands EXCEPT this one:
SELECT @domainID := id FROM civicrm_domain where name = 'Default Domain Name';

and any that start with INSERT INTO civicrm_navigation.

Change the SELECT @domainID line to read:
SET @domainID = 1; (assuming this isn't multi-site).

Then run (after first backing up your database!)
DELETE FROM civicrm_navigation.

Finally, run mysql -u myusername -pmypassword databasename &lt; civicrm_navigation_restore.mysql.