Apple iMac (21.5-inch and 27-inch, Mid 2011) - Manual (Page 49)

49 Chapter 4 Problem, Meet Solution
If your iMac won’t turn on or start up
 Make sure the power cord is plugged into your iMac and a functioning power outlet.
 Restart your computer while holding down the Command (x) and R keys, until the
computer restarts. When the Mac OS X Utilities pane apears, select an option to repair
your disk, restore your software, or reinstall Mac OS X and Apple applications. For
more information, see “Repairing, Restoring, or Reinstalling Mac OS X Software” on
page 50.
 Press the power button (®) and immediately hold down the Command (x),
Option, P, and R keys until you hear the startup sound a second time. This resets the
parameter RAM (PRAM).
 If you recently installed memory, and your iMac sounds tones every five seconds,
make sure that the memory is correctly installed and that it is compatible with your
iMac. Check whether removing the memory you installed allows your iMac to start
up (see page 44).
 Unplug the power cord and wait at least 30 seconds. Plug the power cord in again
and press the power button (®) to start up your iMac.
 If you still can’t start up your iMac, see “Learning More, Service, and Support” on
page 62 for information about contacting Apple for service.
If you have trouble inserting a disc
 Using a continuous motion, push the disc into the drive until your fingers touch the
edge of your iMac.
 Use only a standard-size disc.