I just tested the theme on a test site and the menu works fine. It looks like you’ve made changes to the theme files? That’s not generally a great idea – as your changes will be lost when the theme is updated. Using a child theme is a better way to go:
Aaargh! I don’t have lot of plugins installed, only: contact form 7, nextgen gallery, wp seo, wp google fonts. I don’t wanna start from the beginning. Is there an online debugger that you’d recommend for finding the problem?