Custom Theme: Code is right, Image is loading, But no image is seen.

I’m developing a custom theme for a newspaper.

My header.php:

<div id="top_ad_left"><a href="#"><img src="<?php bloginfo('stylesheet_directory'); ?>/images/ad-top-left.jpg" alt="top-left-ad" width="260" height="90"></a></div>
            <a href="<?php echo home_url(); ?>/" title="<?php bloginfo( 'name' ) ?>" rel="home">
            	<div id="logo"></div>
            </a>
            <div id="top_ad_right"><a href="#"><img src="<?php bloginfo('stylesheet_directory'); ?>/images/ad-top-right.jpg" alt="top-right-ad" width="260" height="90"></a></div>

Here is the CSS:

#top_ad_left{
	float:left;
	position:relative;
	max-width:300px;
	max-height:100px;
	z-index:9999;
	}

#logo{
	background-image: url('images/logo-suprovat.png');
	background-repeat: no-repeat;
	width: 340px;
	height: 60px;
	float:left;
	position:relative;
	margin:0;
	}

#top_ad_right{
	float:right;
	position:relative;
	max-width:300px;
	max-height:100px;
	z-index:9999;
	}

The logo is showing, but the two ad images are not showing.
I checked with Firebug, the images are loading, the got the path exactly as they are. But can’t see them in the front-end.

What’s the problem?