G5 will not turn on
Imac desktop G5 (yes it is ancient) will not turn on. No lights no sound nada. Must admit it has had no power applied for several months. Power supply or hopefully PRAM battery?
iMac Pro
There should be a PMU or SMU reset button on the Logic Board. I forget exactly where this button is located as it has been a long time since I worked on a G5.
If the PRAM battery is bad, then you can remove it to see if the G5 will power on. I believe it should power on without the battery installed.