Can't log out or ctrl-alt-backspace

[TooRight]

I upgraded to Hardy Heron with no problems at all, even got my compwiz desktop effects going in minutes, but one thing that my system will not do is let me log out properly, or even restart the xserver ( by ctrl-alt-backspace). All it does it turn the open windows black and either stall my machine, or else the entire screen goes black and nothing happens until I unplug my comp and start it up again.


Any ideas as to what could be causing this and how I could fix it?

Thanks in advance!