I had a similar problem recently. This turned out not to be a problem with k2 at all, but rather a problem with the template the site owner had purchased.
For whatever reason, the template had the star and social network images in a directory that was not what the joomla template css expected. Since the javascript requires these to be found it appeared that things weren't working. I figured this out using the firebug plugin for firefox, and noticing that there were errors, and seeing what they were.
I was able to correct this by making a couple of symbolic links to the directories that had the actual images, and as soon as the 404 errors were fixed, everything began to work correctly.