Your website is like this:
<div class="navbar-header" style="position:absolute; z-index:2;">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="index.html"><img src="images/logo.png" alt="logo"></a>
</div>
Exchange the position: absolute
for position: relative
It will fit according to the Layout, the way this you force the image to stay there regardless of what happens to the page.
Had stayed like this:
<div class="navbar-header" style="position:relative; z-index:2;">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="index.html"><img src="images/logo.png" alt="logo"></a>
</div>
Note that the error is in the positioning of your Logo and not in the menu, so I saw it works correctly. Put your code so that we can test and help you better, I saw on your site that the image "images/partners/partner_bg.png" is missing too....
– Paulo Roberto
It would be good for you to bring more content to your question, because once you fix your page it will no longer be possible to understand what error was happening and your question will be of no use to anyone but yourself.
– Math