1) Check power outlet. Re-plug power cable.
2) Rest pmu. It is a small button on the logic board.
3) Check poweron battery. Replace if necessary.
4) detach all devices.
Replacing the battery may or may not help. It depends on the model of your mac.
I am not familiar with intricacies of iMac G4.
complete take apart guide.
You can see the battery in section 2.1
Your reply is confusing. Did you read my entire post, including link? If you had, you would find the statement, "After pressing the power on button."
Further, your question, "You did try and turn it back on with the power switch on the side, right?", seems odd. I say this because I suspect my answer to that question would be obvious to 99% of the readers of this discussion. As far as I'm aware, there is no other way to turn on an iMac G4. Do you think that someone with the ability and knowledge to disassemble and reassemble (several times) an iMac G4, would not know they need to use the "power switch on the side", to turn it on?
Also, if you had been reading this discussion carefully, I believe it would have been obvious that anyone who would venture into replacing the iMac G4 battery, would have first eliminated simple things like a bad outlet.
Sorry for the tone here, but my guess it that 99% of the readers, get it.
Replies to such old threads are likely to be a bit curious.
Mostly as to a reason why they are brought up, now.
The link to XLR8 page shows an earlier iMac G4 model
and that is slightly different than the last iMac G4 USB2.0
(15"/17'/20") models. They tend to be more like this inside:
•Mr Totes iMac G4 USB2.0 take apart:
Thermal paste and other steps are required with access
into these layers where the 3.6V 1/2AA lithium battery,
and factory RAM slot, HDD, optical drive, etc, are located.
•3.6V Lithium 1/2AA PRAM clock battery, example:
Also, the 17"/20" can use 2048MB RAM when both slots
get upgraded to 1024MB each, respective to type in each.
The bottom slot uses the same SODIMM as the last iBook
G4 (mid-2005) does, as an upgrade, exact in specification.
The power supply can be tested via small ports in the bottom
under metal plate (by reset button, by airport card slot) to
see if the power supply has failed in one of its voltages.
Anyway, curious to see an old thread come up like this.
In any event...
Good luck & happy computing!