Well, im guessing you want this image to scale and fit the entire horizontal white space. http://codesilver.us/wp-content/themes/SVG/img/slide1-1.jpg
After looking at your code, your .container needs to be 100% width
.container {
width: 100%;
}
After i applied this fix it appears to work, you may want to clean up your div structure a bit overall, but that's a different conversation.
UPDATE: For re sizing you can use the css cover property for background-size: cover; this make sure the image covers the entire div and vertically and horizontally aligns the picture as well.
newheader {
/* background-size: 100px 100px; */
background: url("../img/slide1-1.jpg") no-repeat scroll center center;
margin-top: 5%;
/*background-size*/
-moz-background-size:cover;
background-size:cover;
}