Main menu hidden after WordPress update

Hi,
I uploaded Contact form 7 plug in onto this website: http://www.jpdynamicfitness.com and it said I needed to be running WP 4.0 so I installed it and since then the main menu has disappeared. It’s still there when you go into menus but you can’t see it.

I’ve tried emptying the caches and deactivating / reactivating the plug ins one by one (and have deleted Contact form 7) but it hasn’t reappeared.

Any ideas?

Thank you very much for your help.

Sally.