If the quit button - or the menu - does not appear use Alt+F1 and you should get some "emergency menu" at least in gnome
I have a feeling your xorg.conf got screwed up - please post it (/etc/X11/xorg.conf)
Did you use Envy or the restricted manager?
I always recommend installing the latest Envyhttp://albertomilone.com/nvidia_scripts1.html
It's the legacy version you use for Daryna and earlier
Then install and do configure when Envy asks you