Mac Forum / General / Hardware / August 2007

You did not give enough details. It would be useful with more info on
hardware (what model iMac G4) and what is and is not occurring on boot
attempt (HD spinning, fan running, screen blank, LED on screen on or
blinking, can you boot from a system DVD etc.).

It can be hardware or software.

Software:
IF it boots from DVD your hardware works. Running diagnostic sw to find
where it screws up will work if you are patient enough to explore.
Simple way would be to HOLD down CMD S or V to get single user or
Verbose startup and find what may be screwing up on boot up. SHIFT key
down on boot up prevents extensions from loading at boot which can also
be a problem sometimes.

Brute force would be to reinstall OSX.

Hardware:
bad news would be motherboard and or powersupply dead.

If  you do have any connected peripherals remove them all but keyboard
and mouse.

RAM can also sometimes fail but normally only shows up if you have just
added new RAM and that new RAM might be bad.

At least try:
PRAM reset.  Hold down CMD, Option P & R keys at boot up till chimes
sound 2-3 times.

PMU reset.   Open the USer memory door on bottom, press button on
extreme lower right (on my 17" 1.25GHz iMac G4 gooseneck that is where
it is located). Press it just ONCE. Too many presses can corrupt PMU
again and can drain even a new PRAM battery in days instead of years.

From what you did say, it implies your powersupply fans and HD are all
running.

PRAM battery dead.  These last 4-5 years (some report as long as 7 if
iMac left AC power cord still plugged it when iMac is off).
Unfortunately on my 17" G4 iMac (gooseneck) the battery is located on
the top of the motherboard and more complex disassembly is required to
get to it. A poor design in my way of thinking for the user.

====
Good luck. These are just some thing to try. I am hoping from your
description that the PRAM or PMU reset will get you back in business.

Do think in the future of buying an external firewire hard drive
enclosure and using something like SUperDuper! To clone (copy) a
bootable copy of your running internal boot volume to the external
drive. With regular backups, if anything ever goes wrong with the
internal drive or system, you have a most recent bootable backup right
there on the external drive from which to boot in an emergency.  That
does not help you now, but will be security in the future.

Morenuf

If all it does is beep 3 times and nothing else, may be a hardware
problem.

Is it still under warranty/Applecare? If so call Apple tech support.

You can try resetting the PRAM: Hold down Command-Option-P-R when you
try to start up.

PRAM battery could be dead.