Shutdown the eMac.
Push the power button on the front of the eMac. As soon as the computer begins to start up, press and hold the "Option," "Command," "P" and "R" keys. Continue to hold the keys down until the computer restarts and plays the startup chime for the second time. If this does not reset the PRAM of your eMac, you most likely have an eMac that uses Open Firmware to start up. Turn the eMac off and continue to the next step.
Push the power button and hold it down. The computer will start and boots into the Open Firmware, displaying a "O >" text prompt. Release the power button. If the eMac displays this prompt, skip to Step 5. If it does not display this prompt, proceed to Step 4.
Push the power button. As soon as the eMac begins booting, press and hold the "Option," "Command," "O" and "F" keys until the computer displays the "O >" Open Firmware prompt.
Type the command "reset-nvram" and press "Return."
Type the command "reset-all" and press "Return." The eMac will restart, indicating that you have successfully reset the PRAM.