The use of Disk Utility from the booted OS X Installer Disc, allows you to see more
about the apparently missing hard disk drive; you may be able to see if the hard drive
could be repaired using the Disk Utility. It also could be reformatted, & other options in
that utility are allowed when the computer is not running it system from the hard drive.
Usually a question mark implies there is no system available to the computer, or that
hard drive has failed; or for some reason there is a problem with the format or sectors
have damage, and cannot be read. Without a Destination to install a system, it looks as
though the hard disk drive has failed. But you could see if you can get the Utility to find
it and perhaps repair damages. The 'first aid' portion of Disk Utility may help some; but
if not, you may see if other options in the Disk Utility may help get a rise out of the HDD.
I'd guess the computer needs the internal hard disk drive, replaced. As that G4 model
uses a 2.5-inch ATA-IDE (or parallel-ATA, not SATA) they are available but less common.
There are iFixit.com repair guide pages online, one probably for your exact model iBook.
At the moment, of the several computers I have here, only one PPC G4 is turned on,
and at this time, I'm using an Intel-based Mac, so can't expect the disk utility here to
be similar enough to look further, since 10.4 Tiger is different than 10.9.5 Mavericks.
My older Macs both run Leopard OS X 10.5.8 and are more similar to Tiger 10.4.
With an old Mac or any portable computer, the hard disk drive can fail as they're subject
to a rougher experience than a desktop computer has; figure a portable HDD may last
in active use, as little as a few years.
If you have an externally enclosed FireWire based hard drive with Oxford-type chipset,
it may be possible to use that as a destination, with correct formatting (from install disc)
& be able to attempt to use the portable whose internal hard drive seems to have failed.
{However, such an externally enclosed HDD should also have an external power supply
since it cannot be expected to function (to bootup, etc) before the computer's FW ports
could give it a signal or power. Port-powered external drives are generally a bad idea.}
Also, the battery is also likely bad, they barely last a year or so, if in perfect condition.
OWC macsales is among a few suppliers of quality replacement parts of good repute.
Troubleshooting the computer may be a learning experience, repairing the unit may be
well beyond the level of some people's skill set. However due to the unit not being worth
a whole lot, you could carefully try to fix it using any online guides to replace the HDD
and to determine what else may be the cause of any additional symptoms you may find.
So that's likely the situation you face. Working and repaired examples of older gear may
be found online from actual repair companies or resellers who guaranty their product; &
they can vary in cost. Some you could ship the computer to for a full diagnostic & estimate
and if you don't want it fixed, you're only into it for the shipping. wegenermedia.com and
powerbookmedic.com are a few among several who can repair items, have some for sale
or offer various parts for those who are up to fixing computers. Also ifixit.com guides also
may list some parts and links to sources, from each Mac model repair guide at iFixit site.
Once you get an older PPC Mac running, about the only current browser for it would be
from TenFourFox, that will work in 10.4.11 through 10.5.8 in PowerPC only, not Intel-Mac.
Good luck & happy computing! 🙂