F19 suddenly very unstable

[Frédéric Bron]

Hi,
My F19 has suddenly become very unstable. After about 10 minutes of
running with KDE, the opened windows start to be closed automatically.
I even cannot stop the machine. I have access to the fedora menu but
its rendering is very odd and clicking on shutdown does not do
anything. I cannot go to a terminal either (with konsole which I
cannot start or with Ctrl+Alt+F2).
I have noticed that if I start the computer and just wait at the login
screen of kdm, the keyboard start to not work when I try to type my
login.
I do not know where to look at to find the cause of this.
My F19 is uptodate, with kernel 3.11.7. I have tried to boot with
3.11.6 but experience the same issue.
I have a nvidia video card but I do not use the nvidia driver, the
nouveau one provided by F19 instead.

Thanks for any help,

Frédéric