These instructions will tell you how to reset the PMU and nonvolatile RAM.  

A must for every G5 owner to know before a problem occurs, like if you push the power button and nothing happens or fans operate erratically.

The PMU reset button is located on your logic board, on G5's it's below the front CPU fan assembly, under the memory slots.

 

  1. Unplug the computers power cord and touch the metal case to ground yourself of static electricity.

  2. Slide the front fan assembly straight out towards you.

  3. Press the PMU reset button ONCE!!! Pressing twice could damage logic board and/or battery.

  4. Replace the front CPU fan assembly and the plastic shield.

  5. Wait 10 seconds and plug the power cord back in.

  6. Press the power-on button.


To reset the NVRAM  

Boot holding "option + apple + o + f" until you get a white screen with black text. Upon releasing the keys you are presented with a command prompt.

1. type "reset-nvram" at prompt and press return (will say OK if successful)
2. type "reset-all" at prompt and press return (you will see a quick flash of commands and screen will blank)

Upon completion of step 2 the machine will reboot.

Set your time and preferences in System Preferences.