Omega subtheme - Dropdown menus not working properly
The usual behavior is for sub-menus to only expand when you are on the parent item; so if you have a tree like the one below, you would only see a dropdown containing "Child" when you are on "Parent":


Home

Parent

Child
Child
Child




SOLUTION: 


Go into the menu list links  which is admin/structure/menu/manage/main-menu for the main menu and edit the item you want expanded ("Parent" in this case)
Check the checkbox "Show as expanded"


That item will now be expanded no matter where you are on the site.