Hold down system right system identifier button (rightmost button on front panel) while machine is off as you push the power button (leftmost button)
Blue LEDs will flash– this is the self test
Then, wait until blue LEDs are cycling back and forth, this indicates that the machine is ready to boot. THEN you may let go of the system identifier button.
Then push the system identifier button again –each push will select the next blue light — until the rightmost blue LED is hilited, this indicates that the machine will boot from the optical drive. (This happens to be the first selected light, so to boot from the optical drive, you dont really need to push the SI button again, however, to choose one of the other six boot options you will need to follow this step).