Where is your CSS? (don’t paste it, just post a link to it)
What modifications have you made to the CSS?
If you didn’t paste your CSS into the WP plugins settings page, then let me know which exact file it is in. Searching through a dozen CSS files in your theme trying to find your menu code is not fun.
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[b:9irnh9qr]Things which make me grumpy:[/b:9irnh9qr]
Not telling me you modified part of the CSS.
You have some bizarre CSS code in there such as cleared floats on list items. I can’t imagine it would be possible to get a dropdown menu working if you are trying to clear parts of the menu like that.