It sounds like you are not the main admin user and don't have permission in MODX to see that tab. If you have access through PhpMyAdmin, you could change your user role to match the admin one. It's also possible, though unlikely, that you have the right to alter your permissions.
Otherwise, it will be up to whoever is the real admin.
The best guess on why the code no longer works is that the host has upgraded PHP and the code contains deprecated functions. There may be clues in the error log, if you can see it.
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PLEASE, PLEASE specify the version of MODX you are using . . . PLEASE!
MODx info for everyone:
http://bobsguides.com/MODx.html