The occasional unresponsive application has become such a part of OS X life that, among the Mac cognoscenti online, the dreaded, endless “please wait” cursor has been given its own acronym: SBOD (Spinning Beachball of Death). When the SBOD strikes, no amount of mouse clicking and keyboard pounding will get you out of the recalcitrant program.
Here are the different ways you can go about force quitting a stuck program (the equivalent of pressing Ctrl+Alt+Delete in Windows), in increasing order of desperation:
Force quit the usual way. Choose
→Force Quit to terminate the stuck program, or use one of the other force-quit methods described on Force Quitting Programs.Force quit the sneaky way. Some programs, including the Dock, don’t show up at all in the usual Force Quit dialog box. Your next attempt, therefore, should be to open the Activity Monitor program (in Applications→Utilities), which shows everything that’s running. Double-click a program and then, in the resulting dialog box, click Quit to force quit it. (Unix hounds: You can also use the kill command in Terminal.)
Force quit remotely. If the Finder itself has locked up, you can’t very well get to Activity Monitor (unless it occurred to you beforehand to stash its icon in your Dock—not a bad idea). At this point, you may have to abort the locked program from another computer across the network, if you’re on one, by using the SSH (secure shell) command. Remote Control Program Killing offers a blow-by-blow description of how you might terminate a program by remote control in this way, either from elsewhere on the office network or even from across the Internet.