Go to "Edit your listing" then "Listing Designer" then check the check-box beside "Add a theme". This will download a list of available themes (may take 5 to 10 secs). After you select a theme you can select a design (again may take 5 to 10 secs). You have to give time as the page updates any change.
Well, I don't know why its not working with you. Its working well with me & others hopefully. Just want to mention that I use Opera browser. If you got one, why not try on it.
I think I have solved your problem. Guess what? You just need to update your Java software, thats it. Open Control Panel and you see the Java icon. Open it and run an update.