Apple IMac - Whats Included in the iMac Box

Hot Issues Forcing a Restart - 6
Forcing a Restart
If holding down the Command, Control and Power keys fails
to restart the iMac computer after a system hang, you can
force a restart in one of two ways:
First, try inserting a straightened paper clip in the reset
button hole. (Open the I/O door on the side of the iMac. The
reset button hole is the top hole located between the Ethernet
and modem ports and marked with a triangle symbol.)
If the reset button method doesn’t work, try the following:
1 Unplug the power cord.
2 Wait at least 30 seconds and then reconnect the power
cord.
3 Restart the iMac by pressing the power button on either
the keyboard or the front of the computer.