Background Image not shown I use the Bluemaster theme for my site. Since I installed this theme, it worked well, but
a few days ago the background image was not shown.

I think this is because there are a large photo in background.
How do I fix this problem?
Your css is the problem.   There is no images/bg.gif.  There is an image/bg.png file.

Change

body {
    background: url("images/bg.gif") repeat scroll 0 0 transparent;
    color: #666666;
    font-family: Tahoma;
    font-size: 12px;
    padding: 0;
    text-align: center;
}


to:

body {
    background: url("images/bg.png") repeat scroll 0 0 transparent;
    color: #666666;
    font-family: Tahoma;
    font-size: 12px;
    padding: 0;
    text-align: center;
}