Menu Bar Dysfunction

My website was working fine up until last week. Now I am having issues.

The menu bar at the top of my webpage has drop down categories within each header. When you click on the individual categories it goes to a list of blog posts. But when you click on the main header button nothing appears as it did previously.

My webpage is http://www.hannahtangerine.com. Any insights will be much appreciated. I have a hunch that it could be due to a recent WP upgrade. What do YOU think?

THANKS.