Comment 13 for bug 367767

For Dibya Sanyal...this is not a fix for the bug, just a work around so you don't have to hard reboot.

If you hold down the alt and scroll lock (sysreq) keys and while holding them down, press k, you should restart x without having to reboot.

This can also be set back to the old standard of ctrl / alt / backspace in Karmic by going to System > Preferences > Keyboard and then on the Layouts tab, Click on "Layout Options" and you will see a list of items. Click the triangle next to "key sequence to kill the x server" and put a check mark in the box next to "Control + Alt + Backspace" box, then click close.

If all this does not work, a safe way to force a reboot is to again hold down the alt and scroll lock (sysreq) keys and while holding them down, press in sequence, r s e i u b. Even when the system appears totally locked up, this "should" work.