Ok, now I see. You’ve added the same menu on both navigation bars, then you’ve hid the one from navigation bar above header. If you want the menu only on one navigation bar, but it appear on both, go at Appearance -> Menus and edit the desired menu. Assign it to both navigation bars -> Save. Re-assign the menu only to desired navigation bar (un-tick the other navigation bar) -> Save.
Now the menu will be assigned in correct position so, go at Suffusion Options -> Back-end -> Custom Includes -> Custom Styles and comment the code with display:none
which hide #nav-top
.
In fact, better is to comment all the codes referring to #nav and #nav-top from your Custom Styles and let the menus as default to see what’s happens. After the collapsing menu will work, you can uncomment these lines.
Also, try to select “Auto-generate the CSS and print it in the HTML source (Least load on server, ugly page source code)” at the first option from Suffusion Options -> Backend -> Site Optimization to dynamically generate the CSS and not use a file which can be eventually cached.