What is 'connection button'? Where did you find it and you added it to what toolbar?
I have never worked with accde/mde files. Apparently this one was created without the navigation pane hidden. Why it would be exposed on de but not db file escapes me.
If you hold down the shift key while opening the accdb/mdb file, should override most project settings. Even if you don't see an expanded navigation pane with objects listed, do you at least see a vertical bar with the words 'Navigation Pane'?
Try F11 to reveal the navigation pane.
Did you try the import exercise?
If the front and back ends are both Access files, don't need an ODBC data source set up. Links to tables are managed within Access.