o, Frostwire, is probably the default one,, You can try doing this un-install frostwire, and open a download and see if it opens with Utorrent, or un-install both, and then re-install Utorrent first, and try.
Don't TRY THOSE STEPS ABOVE FIRST, TRY GOING TO THIS SITE --->> http://www.utorrent.com/forum/viewtopic.php?id=6525