looking at your screenshot - it seems you don't have a theme. you need to link to the appropriate css for one of dijit's themes and then add the theme name as a class to the body of your html.
also, you should probably only set the store for the StoreExplorer after you create the store.
you could avoid your xhrGet by giving the url to the store directly.
take a look at the store explorer test page if you haven't done so already.