[Opserty]

Disable any other modifications you may have installed on your board if it still does not appear try creating a New Style with no Parent style and see if this resolves the issue.

Try accessing direct files like yourdomain.com/forums/index.php it maybe that the server is misconfigured or something like that so isn't displaying correctly.

Furthermore if you have done any edits to default vBulletin files you will probably need to undo these or overwrite the files with a fresh copy (keeping a backup of the old ones).