Dead IMac

There is some chance the hard disk drive may have failed and
so in the processes involved, maybe the data on that drive was
corrupted in such a way as to affect the other startup sequences.

{You say you tried to connect via FireWire to a laptop and that
did not work; and I'm assuming the method attempted was a
rather known one involving FireWire Target Disk mode, and
the suspect computer was first booted in T-disk mode, then a
FW cable was attached to the other running Mac computer.}

The power management reset can sometimes help if the Mac
has a related problem; but a clicking often indicates a bad drive.

At some point, if the issue involves a failure on the logic board,
other components may also appear to fail; if or when that's so.
Further testing or troubleshooting is probably warranted; but a
path to do so, without other test hardware or software, is limited.

Perhaps one of the other contributors here who are more active
in repair and troubleshooting these older iMac G4s and iBooks,
may be able to give you ideas on how to proceed at this point.

Good luck & happy computing! 🙂

• How to use and troubleshoot FireWire target disk mode (TDM)
http://support.apple.com/kb/HT1661

When the suspect computer is running in TDM, an attached computer
can see its hard disk drive (or if really damaged, not) and it may be
possible to attempt accessing the failing computer's drive to recover
data, or to use disk utilities - including third-party ones, ie DiskWarrior,
to see if the low-level damages could be repaired just to retrieve data.

The computer started up in FW TDM won't do much else; there are
some troubleshooting and repair possibilities available in using this.
Be sure, if you can do this, the correct computer is running in TDM.
Some users mistakenly start the healthy computer in target disk mode
and then wonder why the process does not get anywhere.

And some users had found in their circumstances, with skill & familiarity,
they were able to clone a failing OS X to another hard disk drive, and
save content, even though that system was not able to boot the computer.
If the physical hard disk drive has ceased to function, that may not work.

What is your second computer? Assuming you are online with another Mac.

(In other situations, TDM can be used creatively when both computers
have FireWire ports and the correct cable is used to connect them.)

Also, if you had an externally enclosed hard disk drive in a FireWire
case, it may be possible to do more; without a working optical drive
in the computer, most of the simple processes become harder. A Mac
can be run from an external clone of correct OS, on bootable ext. HDD.

PS: There is a difference in the reference words "disk" vs. "disc."

Perhaps one of the contributing tech persons who diagnose & fix these
for fun or vocation, will see your post and add some content I failed to.

Good luck & happy computing! 🙂

{ edited 2x }

Generally, there is very limited to no additional access into some of the computer's
other hardware when booted into FW TDM. In some computers, the optical drive
may be accessed (in a healthy Mac) and of those models, some can allow use of
the healthy computer's optical drive from a computer whose hardware may not
have a Superdrive. The need for that could occur if one is trying to install an OS
that shipped on a DVD, in a computer whose hardware was only a CD-ROM drive.

This probably won't help get into your computer; and in some cases, there may be
some problems in using FW TDM between Intel-based Macs and PPC-based Macs.

Did you get around to resetting the power management unit? The button is in hiding
under the metal bottom plate and certain rules apply when resetting that PMU:

• Resetting the iMac (flat panel G4) Power Management Unit (PMU)
http://support.apple.com/kb/HT1712?viewlocale=en_US

• Resetting your Mac's PRAM and NVRAM:
http://support.apple.com/kb/HT1379?viewlocale=en_US

There are several reasons why the computer may hang on partial startup, if the
hard disk drive has a damaged section of data on the drive and it can't go past it.
Sometimes, the display may not work; other times it could.

This is a gray area of activity or inactivity; and some of these kinds of overlapping
questions are answered in Apple Support documents; found by searching Support
or sometimes by searching via Google or other search engine, very selectively.

Words such as ' black screen startup ' or ' chime no display startup ' and other words
such as iMac G4 and so on. There can be dozens of results; some won't be for an
iMac G4 and others may be for a G4 tower, etc. I've found many answers to issues
among searching; & before I had reliable internet, I repaired dozens of Macs without
the internet - and not much of a tech library. Trial and error served me adequately.

If you search these forums for replies and questions similar to yours, you would very
likely find some answers or perhaps links to Support Documents or articles on topic.

There is some chance there may be some problem outside of the hard disk drive;
as these machines age, other issues that have become known in general surface.
Some get a problem in the graphics circuitry and there are replaceable parts that
can be installed. In a few cases, the graphic card or video unit may fail and since
it is essentially part of the logic board, that would constitute a major failure (cost.)

I was hoping someone such as Mr Totes, or spudnutty, among others - would see
your thread and add their experienced comments - where mine are lacking.

One can always hope...
Good luck & happy computing! 🙂

PS: You would have to find the user account files in order to access content on
the failed Mac in Target Disk Mode, and try to copy the user content into a folder
in the healthy computer; or perhaps also burn the images, etc. to blank CD/DVDs.

There are those cables between the main lower unit and the LCD
panel; that is often replaced as a unit including the wires inside.

{I'm not certain how to go about checking the individual connections;
perhaps someone who has experience in these will reply...}

Another area could be the Inverter; there also is some other part(s)
inside the LCD panel casing that may affect the visual display output.

Electronic components and wires; outside of the graphics processor
card (that is on the logic board and essentially is not separate) and
since you lucked out in checking the output of the external video port
to find there still is output, there is a greater degree of hope.

And if the inverter or other smaller part is at fault for the main display,
the cost should be affordable. There may even be a take-apart page
on the internet showing how to do some of these other tasks.

The contributor names mentioned in a previous post would still be
good sources of information; so if Spudnutty (richard) or Mr Totes
should be available to offer their advice, either one has experience.
I may be able to email the former and suggest he look into your post;
but can't say if that would be successful or not. He is also very busy.

Some iMac G4 users whose computers LCD circuitry failed, had
taken them apart and ran them "headless" but that is not necessary
when the output of the video graphics appears sound.

Were you able to detect any hint of data on the main display, in the
dark shadows of the blank/black display? If the LCD is dark, the
data may still be getting there but the backlight may be off due to
one or more defective parts. If you can see a desktop in the dark
display by use of a flashlight, then there are circuits that may be
not too hard to fix; standard parts and procedures.

For the most part, the actual backlights (two) usually don't go out.
The circuitry to them, inverters and other stuff, like flexing wires,
are among the more likely candidates as a cause of this issue.

Hopefully the matter is only an inverter or other similar circuit/wire.
It's been awhile since I looked into diagrams on how these iMac G4s
were built, some show the part numbers in the panel, with the LCD.

Good luck & happy computing! 🙂

The design of these iMac G4s is such that simply looking into
the bottom of one, probably won't do much to tell if a wire is
bad or not. The kinds of circuits contributing to a display failure
would be more integrated and in the upper part of the unit.

In order to explore or at least see without taking one apart, a
complete expanded view of the components is recommended.
And if you can find an original service manual such as a tech
would be trained to use, in order to troubleshoot & repair these,
that would be only the beginning. At least to see the placement
of the parts without opening the case is a good idea, first.

The video circuits inside the display area and wires connecting
into the base unit are generally not accessible in a simple way.
One of the suspect parts is the Inverter, there also are others,
to include cables in the flexible chrome arm.

See an exploded view with part numbers here (reference only)
http://www.mac-pro.com/Mac-Pro-Online-Store/G4-iMac-USB-2-0-Parts

There may be a way to search for troubleshooting display issues
and find articles from other sites and users who may or may not
have technical experience and skill, to get further insight into this
and there had been some posts in Apple Discussions regarding
similar topics, with links to off-site images and helpful hints. To
find them as time goes on, may be increasingly difficult, now.

Taking the base off one of these without technical experience,
knowledge, or skills, and attempting to fix this kind of issue, is
not a recommended course of action; learning more first, is.
Plus, the bottom plate is far from away from the inverter circuit
which is inside the LCD panel housing. (see expanded view.)

Good luck & happy computing! 🙂