There is a distinct possibility the hard disk drive is failing... Have you tried startup via
use of the install-restore DVD Tiger 10.4? That may give you opportunity to see if
you can run the computer (from that reduced boot volume) and then consider maybe
to see if Disk Utility can fix the hard drive. However most likely, the HDD is worn/failing.
Or some other issue may result in the situation, since there are circuit board items
that have been known to fail; at some point you may need to consider another old
vintage computer (if you can find one, in repaired working order) if you need to run
the vintage software and older applications. Sometimes, repaired older portable Mac
PPC units may be found at places such as http://wegenermedia.com for a fair price.
If you have an external backup, clone, or other archives of important files, you may be
able to find instruction online on how to replace the internal hard disk drive; if you can
find an IDE/ATA (not newer SATA) the older model is sometimes referred to as P/ATA
or parallel ATA. Getting into these older iBook & powerbook models can be trouble, as
there are parts, wires, & bits that are in the way; so damage to other parts may occur.
The iFixit.com mac repair guides include older PowerPC portable, iBook G4, & others.
To have a complete boot-capable full system clone on an externally enclosed HDD is
a fair way to restore; but once the internal hard drive fails, recovering data is difficult.
• How to use and troubleshoot FireWire target disk mode - Apple Support
Not sure what else to say. You may be able to start the computer in Target Disk mode
so another computer with FireWire port could allow you to see & perhaps copy off the
content to another archive, via a working computer. (You'd try to start the failing Mac
by use of T-key on startup; follow target disk mode instructions to see it as a drive.)
Is your other Mac one with FireWire ports? Some later Intel-based Macs haven't FW.
Newer intel-based Mac could use an adapter cable, if they have Thunderbolt port.
Hopefully you can save content, then replace the failed HDD; if that's the cause of issue.
One of my older PPC portables could use new larger capacity HDD; something quicker.
Good luck & happy computing!