Reset your PRAM. Press and hold down the Command Option P R keys while starting your computer. You will hear the startup chime. continue holding down those keys until you hear the startup chime a second time. Release the keys. If the computer restarts, you will need to reset your Date and Time. It might be time to replace your PRAM battery. The G5 iMacs require a 3 volt CR2032 lithium watch/camera battery like below:
You can find these batteries at Walmart, Kmart, Target, most local drugstore chains, for between $3-$5, or at Radio Shack for $12-$20.
If you have any G5 iMac model EXCEPT the iSight version, you can probably do the battery install yourself. Watch this video on upgrading your iMac's RAM to show you how to remove the back of your iMac, if you don't already know how:
While you have the back off, use a can of compressed air to blow the dust out the vents at the bottom of the iMac, the fans, and anywhere else you can. Also inspect the 28-30 capacitors on the logic board. Look for dark spots, if they look puffy or swollen, or leaks.
Reset the SMC by removing all cables (USB, Firewire, Ethernet, Modem, Power cord) from the back of your computer. Let it sit for one minute. Press and hold the power on button on the back of the iMac while plugging in the power cord. Release the power on button. Count to five, the press the power on button again.
Place your original, came with the iMac when purchased install disk, into the slot on the iMac, press and hold the C key while pressing the power on button on the back of the computer. (If you have upgraded your OS from when you purchased your iMac, example your iMac came with OS 10.3 installed, and you're now using OS 10.5, then use the OS 10.5 Retail Install disk that you had used to upgrade your OS instead of the original, came with the iMac disk.)
Continue holding the C key until you see the OS starting to load. DO NOT do an OS installation. At the top Menu bar, select Utilities or Utility, and pull down to Disk Utility. On the left side of the window that opens,select your normal OS drive. Click First Aid at the top middle of the window if it isn't already selected. Click Repair Disk from the lower right area of the window. When that is done, click Repair Permissions to the left of the Repair Disk button you clicked earlier.
When that is done, quit Disk Utility. From the top Menu bar (I think its under Utilities) select the Start Up Manager, and choose your normal boot volume as the startup disk. Restart the computer. If successful, and you've rebooted from your normal startup disk, eject the install DVD/CD, and you're good to go.
Quick report on progress so far... I've tried the option 1 process above insofar as to try the restart. The process seemed to work okay, but then I did find after a while that the machine shut down and stayed down despite attempts to restart for some time (4 hours or so).
However, it had shut itself down before that once, and so I also tried option 2 on one of the restarts. As I say, however, there was then a longer shut down after that.
After waiting a few hours during which time the machine would not start up, I then gave it another try. It started up and is running now. I have a feeling, though, that eventually it will shut down again. So, I'm guessing that replacing the PRAM battery would be a good bet.
Since I haven't ever opened up my iMac, I'm a little nervous about doing something that could cause additional problems. Not used to creating a static free surface, etc. But as you've outlined it, the process certainly seems relatively simple. Or am I mistaken?
I'll report further when I see what happens.
Thanks for your help so far.
I hate to be the possible bringer of bad news, but iMac G5's were suspectible to failing capacitors. When a capacitior would fail or begin to fail, it would experience issues like that.
That is an example of what it will look like if it fails.
I had occasion to purchase many iMac G5's from a business that was shutting down its American office, for use in a home business network.
Many of these did fail in exactly the way you specified and the problem was indeed bad capacitors.
I was lucky at that time, about 2010, and was able to get the Genius Bar at my local Apple Store to fix them for no cost, even though Apple's extended warranty for this problem was long past. It is doubtful that at this late date, Apple even carries any of the motherboards for these Macs anymore.
Quite honestly, when my last iMac G5 died in 2011 (hard disk crash, after replacing a power supply in 2010; but good capacitors), I decided it was time to move on and replaced it with the mid-2011 Mac Mini, and other than the loss of Rosetta (this model comes with OS X Lion 10.7), I am very happy with the replacement.
For Rosetta, I installed Snow Leopard (with Rosetta) into Parallels and have PowerPC application functionality concurrently with Lion when I need it.
NOTE: The link to the photobucket seems to be broken, and when fixed, the photo was deleted by the poster:
Hmm. Sounds like tricky business. I guess my question as I go into talking with local tech repair folks is whether replacing capacitors is a worthwhile fix or whether their being damaged likely means a problem with the motherboard as well. Do techs typically deal with things like replacing capacitors?
You don't say where "local" is; but here in Los Angeles there are some third party shops that will do motherboard component repairs. Apple ALWAYS only did board replacements and/or complete swaps.
I would say that you should not spend the cost required for a component fix given the fact that something else will clearly fail soon afterwards (as was my experience, even with good capacitors).
Buy a new Mac Mini: for that price you get a more powerful CPU, more RAM, more HD space and Mountain Lion (not always a plus according to some people).
"Tricky business" - not sure what you are referring to here...
I'm in PA.
What I meant by tricky business was the nature of the capacitor problem and its relationship to other matters. I might have some friends who would take it on as "a project" without the cost being too high, but maybe it's not even worth that. I've love to be able to keep the big screen, I guess, but that's not the be all.
I appreciate your advice on the Mac Mini, though. Might be the most sensible thing in the end.
When their done with your tricky business, I got my Panasonic 42" Plasma I could send them: it went black while I was watching it and now the red LED blinks ten times; which the local Panny service facility says could be one of four different boards. But I think it is BAD CAPACITORS!!!
Now I am down to watching on my backup: 22" Samsung LCD Monitor/TV - I just sit A LOT CLOSER!
I continue to try to get a fuller understanding of the exact symptoms the machine is exhibiting before I turn the machine over to someone to experiment on.
After shutting it down for a week or so, I rebooted a little over a day ago. Once it was running (without requiring any login as it should, by the way), I put the machine to sleep. It's be quietly snoozing now for over a day. No shut down. It used to even shut down when asleep. However, I didn't open any programs when I rebooted it, so maybe that's where the shut down gets activated.
I still have a few experiments I'll try. Letting it run without programs open but without being fully asleep. Letting it sleep with a program (or two or three) running. I mean, it's a doorstop for now, so I guess I'll try some of this stuff while I save some money to buy a new one. I'll be curious to see what happens.