I ssh in as root to a PC with a problem and fix it remotely too.

But there are alternatives to this on the self same PC you're experiencing problems with.

(1) <ctrl><alt><backspace> will log you out of your current session and bring back the login screen on a hdinstalled PC or restart KDE on a cdboot.

(2) <ctrl><alt><f1> will let you login on a text console as root. There you can run top to identify the offending pid. Then kill it!

HTH,
AJG