gdm -ask password - nouveau - black screen
as far as I know, there is nouveau driver available. The closed source one n testing. I did not manage to install it from testing (yum wants me to update kernel). Moreover I had several 'no signal' situations on monitor (no ctrl-alt-fn worked) during <gdm -> switching user -> ask password dialog>. When I kill remotely askpasswd (some name like this), all gdm restarts, I loose all sessions and the screen is back. It is randomly reproducible.