7

A2003: "Tools" / "Startup" / "Allow Build-in Toolbars"

A2007: "Office Button" / Button "Access Options" / "Current Database" / "Ribbon and Toolbar Options" / "Allow Build-in Toolbars"

Select your menubar from the drop-down "Menu Bar".
 

If you open your database this way the built-in ribbons will not be shown, only your menubar: