Apple iMac (21.5-inch and 27-inch, Mid 2010) - Manual (Page 54)

54 Chapter 4 Problem, Meet Solution
When an Application Doesn’t Respond
On rare occasion, an application may “freeze.” Mac OS X provides a way to quit an
application that’s not responding, without restarting your iMac. Quitting a frozen
application may allow you to save your work in other open applications.
To force an application to quit:
1 Press Command (x)-Option-Esc or choose Apple () > Force Quit.
The Force Quit Applications dialog appears with the application selected.
2 Click Force Quit.
The application quits, leaving all other applications open.
Reinstalling the Software That Came with Your iMac
Use the software installation discs that came with your iMac to reinstall Mac OS X and
any applications that came with your computer.
Important: Apple recommends that you back up the data on your hard disk before
restoring software. Apple is not responsible for any lost data.
Installing Mac OS X
To install Mac OS X:
1 Back up your essential files.
2 Insert the Mac OS X Install DVD that came with your iMac.