imac g4 won't start

Dust could have gotten in the unit and is preventing it from starting up. Unfortunately to really clean the dust you need a special neck tool to ensure that the neck is reattached smoothly. Check around for a local authorized service technician who might still have those tools in stock and they can check if it is worth fixing.

This is a late post, but thought it might be helpful to someone.

Are any or all of these your symptoms?

-- dead iMac after disconnect from power outlet

-- replace battery but computer still dead

-- re-open computer, check cabling, etc., but still nothing

So, I thought my iMac was dead. But found others on the 'net talking about letting computer sit (with power cord plugged in) for 24 hours (or more) and then they were able to boot their computer.

Well, after my failure with the new battery, etc., I let my computer sit for approx 24 hrs (with new battery), power cord plugged in, and viola. After pressing the power on button, first some low level internal sounds, then a loud odd chime (not the standard), and within 15 - 20 seconds, that beautiful boot chime and computer back to normal.

I have yet to try unplugging power, so cannot report on that.

I'm actually an EE, but not in the electronics field, yet my gut tells me many of the mac computer products have some funky power management stuff. I'm guessing a long-dead battery does something weird that requires another weird kind of "charging", hence the fix with the 24 hour sit period. Just a relatively wild guess.

The reason for my post is to say, if you replace the battery, do not give up (I almost did). Try the 24+ sit with power plugged in.