Dropdown category doesn't work

Please provide the site url along with the site login details for the admins to look into it in greater details.

Please send me username & password of your site (via private answer) for further checking.

Firstly, please deactivate  all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one and let us know if you find the problematic plugin(s). Maybe there is a conflict in plugins.
Hope this helps !

i have the same problem.
After some css editting the dropdown is not working anymore.
links: http://yes.welovestoer.nl

To resolve this issue. Firstly, follow the jetpack’s guideline in the Blog article on how to use Edit CSS here. http://cmspioneer.com/designwall/blog/using-jetpack-custom-css-for-your-wordpress-site/
Then add the code to the Edit Css.

#nav .menu ul li {
    margin: 0;    
}

#nav .menu li:hover > ul {
    clip: rect(-1px, 1000px, 1000px, 0px);
    margin: 0;
    opacity: 1;
}
#nav .menu ul {
    width: auto;
}

#nav .menu ul ul {
    left: 200px;
    margin: -1px 0 0 20px !important;
}

If you still face there issue, you can send me username & password of your site (via private answer) for further checking.
Hope this helps !