IMac G4 won't boot up after being unplugged for a week

Question

Last weekend we took our 7-year old iMac temporarily out of service while having some remodeling done. Peripherals were disconnected and everything was packed away safely in boxes.
Today, I tried to set our system back up in the same place, using the same electrical outlets, etc. Everything else (DSL modem, Airport Extreme, deskjet printer) is powering up OK and working just fine. However, the iMac itself will not power up at all -- no chime, no fan sound, screen remains dark -- when the power button is depressed.
The power button does not appear to be stuck, as far as I can see. I've tried disconnecting power for over five minutes, disconnecting the keyboard and mouse and other peripherals, using a different outlet. Still nothing. (I haven't tried using a different power cord because I don't have another one that fits.)
Everything was working fine last week before we took the system down.
Any ideas?

Answer 1

Hey Henry,
Several years ago, someone (cough) managed to strip the head off one of the screws while trying to take off the base panel, and I'm not sure it's possible to get into it without special power tools.
Well you need to get in there to at least press the PMU button.
So depending on how stripped the head is you could use a jeweler's straight slot screw driver. What you're trying to do is to press and rock the tip in the stripped area, which will usually be conical, cutting a new groove into the "cone" to get enough purchase to extract the screw.
I have also used a Dremel type tool to cut a new slot. Using the thinnest cutoff disk I'd grind it down on a piece of scrap steel until the diameter is close to but slightly over the head of the screw. Approach the head of the screw from the outer radial direction and use the reduced disk to cut a new slot in the head of the screw. Then use your straight slot screw driver to extract the screw.
There are miniature "Easy Out" type extraction devices that can also do this job but you can only buy them from special distributors.
The last resort is to drill the screw head with a .073" or larger bit to break the head off the screw shank. The shank is .072" in diameter.
OK so with the bottom off here's the diagnostic for a no power situation from the service manual:
"6. Reset PMU. Refer to “Resetting the PMU on the Logic Board” mentioned earlier in this chapter or Kbase article 95165."
The PMU button is on the opposite side of the RAM slot and towards the bottom under some plastic. Only press it once and have the unit unplugged.
"7. Verify the battery is good before replacing modules. A drained battery may be indicative of a crashed Power Management Unit. Does the battery measure at least +3.5v? If not, replace the battery and reset the PMU. If the battery does measure over +3.5v, reinstall the battery and reset the PMU."
Richard