ارجو حل

.header_c {
    background-image: url(http://i57.servimg.com/u/f57/16/80/02/94/bcsja10.gif);
    background-repeat: no-repeat;
    height: 320px;
    margin-left: auto;
    margin-right: auto;
    position: relative;
    width: 636px;
}