.centerDiv{
	width:968px;
	height:600px;
	background:#ccc;
	position:absolute;
	margin-top:-300px;
	margin-left:-484px;
	top:50%;
	left:50%;
}

Here's a simple way to get your div always on center in any screen size.
margins should be half of width and height.

vertical horizontal centered div

center

CSS