Gnome freezes in FC6

[Van <vanyel medusa bioc aecom yu edu>]

Every so often, my Fedora freezes. I've come to realize that it's only 
the GNOME interface that actually freezes. I'm running Fedora in a 
Parallels VM. I can ssh into the VM from my outside Mac and even pop 
X-sessions from it, but I no longer have mouse or keyboard control of 
Fedora's GNOME Desktop itself. Occasionally if I use ps -aux and choose 
some graphical process (i.e. like Thunderbird or Firefox or an open 
terminal window) and kill it, it "jump starts" GNOME and I get control 
back. But this is "iffy" at best. Usually I just end up doing a "skill 
-KILL -u van" and then logging back in.

Anyone have a clue as to what could be causing this and how I can fix 
it? I don't know where to begin to troubleshoot this.

Van