Menu Issue

My menu is not working correctly. The menu should drop down and show at least one or more page on each. If I add a new page it doesn’t show up either, it is just those four pages. When I do a view source I can see the links, they just don’t show up on the page. If I switch to another theme everything works fine. I would like to use this theme but the menu needs to work. Where should I start looking?

https://allcomputercertifications.com/wordpress/