I have a little problem with the horizontal menu that I implemented for the website. The menu contains only three items, but when viewed on a large widescreen monitor, the last item crashes onto a new line. I cannot verify this myself, since the widescreen monitor is used by my client, and so far I cannot reproduce the error, she sent me this screenshot.

The client uses Internet Explorer 8 on Windows 7, and I tested this browser and OS on a regular size monitor that seems to work. It seems to be a widescreen screen.
This is what the page looks like on my screen and on each subsequent screen that I tested on.

Here is the code I have for the menu.
HTML
<div class="menu">
<ul class="nav">
<li class="nav-item" id="first-item"><a href="/why-us.php">WHY US</a></li>
<li class="nav-item"><a href="/links.php">LINKS</a></li>
<li class="nav-item"><a href="/contact.php">CONTACT</a></li>
</ul>
</div>
CSS
.nav-item {
font-size:2em;
margin-left:175px;
}
.nav-item a {
color:#2B2F73;
}
.nav {
list-style-type:none;
padding:0;
margin:auto;
width:744px;
}
.nav li {
list-style-type:none;
float:left;
display:inline;
}
#first-item {
margin-left:0px !important;
}
.menu {
width:960px;
height:40px;
margin:auto;
}
- - , ?