You many not actually be able to hover the mouse rightaway. Instead, you might have to chain all the actions together. So, first hover to the element that reveals the others (dropdown), then during the same chain, move to the visible element you want to click and simply click on it.
So, when your working with Action Chains, you need to remember to 'do it like a user would'.
Actions action = new Actions(webdriver);
WebElement element = webdriver.findElement(By.xpath("html/body/div/ul/li/a"));
Hope this helps!
Check out this selenium online training to learn more about it.