Sorry beyond my scope then as I am out of ideas.

I did do a quick search and found an old thread where someone had similar menu problems.

See www.zen-cart.com/forum/showthread.php?p=521167 and look at post 4.

When you click any of your main menu options so the "site map" view appears do you then have the GV menu?

If you do you may want to check for missing files as Ajeh suggested.

Beyond that sorry tried my best!