In the Database Browser, it notes the server but does not note any database under it. There is no [+] to expand and display. But there are databases in that server and they are noted in the tnsnames.ora file. There are no problems with connecting to these databases and no problems working with other features in Toad (with these databases).
DatabaseBrowser.tdb not updated correctly.
Rename the DatabaseBrowser.tdb file to force Toad to rebuild it.
Exit Toad, go to the application data directory, User Files (i.e. C:\Documents and Settings\<personal folder>\Application Data\Quest Software\Toad for Oracle\<version>\User Files) and rename DatabaseBrowser.tdb.
Restart Toad and test the issue.