On a PC, Crt-Alt-Delete (A.K.A. the Three Finger Salute) is a keyboard shortcut that just about everybody knows. If you need to kill something that isn't running, then thats usually the solution.

The Mac has an equivalent - Command-Option-Escape, which brings up a window to let you force-quit an application.

I've been using a Mac for about four and a half years. But I have to Google for that key combination every time I have to use it, because I've only had to use it about four times.