Yep it's because you have the image set as a background. The site below shows you how to turn a background image into a hyperlink...
http://www.attackr.com/css-trick-tur...lickable-link/
The other option is to edit your stylesheet header area and delete the CSS code that is making it a background image and open your header file and just link to it using a regular <img tag. Then of course you can make it a hyperlink like normal HTML.
Does that make sense? There's probably a better way of explaining this.