After upgrading to Fedora 12 from Fedora 11, the file manager does not work. In otherwords the stuff on the desktop and home directory does not appear.
The solution was to remove gstream "bad" and "ugly" codecs. Restart the machine. Then install the gstream "bad" and "ugly" codecs.
Once that was done, all are ok.
Got the above information from the following,
http://forums.fedoraforum.org/showthread.php?t=237408&highlight=file+manager