Don’t know much about using geoserver, but just as a general debugging tip, OpenLayers allows you to right-click and find the URL of an image (if it has managed to load an image at all) so try that on the white map. Then try the URL directly in your address bar. You might see something wrong in the URL which will help you debug a problem in OpenLayers initialisation, although generally WMS URLs are fairly massive! You could also try WMS GetCapabilities request direct in your browser (just to see if it works, but also might reveal something useful)
Anyone else know more about OpenLayers <–> geoserver ?