Blue screen on start up, even in safe mode, common fixes not working

Question

I did quite a bit of searching for the problem I'm having, and it seems some of the symptoms are common, but none of the various fixes I've come across have worked. Any help pointing to other things to try would be appreciated, as it is getting harder to search for things without finding repeats of what I've already tried. Also, I was going to post this on the OSX 10.4 board, but changes in symptoms (mentioned at the end of this post) are starting to make me think this could be a hardware issue.
The main problem is that my computer boots normally until the blue screen just before the login window should appear, then hangs.
My system: iBook G4, 800 MHz, running 10.4.11, has an extra GB of RAM installed (for a total of 1.1 GB), new hard drive that is less than a year old.
Things I've tried:
Booting in safe mode: No change, still hangs at blue screen.
Removing airport card, and extra ram has no effect.
I've done a PRAM reset
I've done a PSU reset
Checked for file system and permissions errors with Disk Utility on OS CD
Booting into single user mode works fine, where I tried:
fsck -fy, no errors reported
running /etc/rc worked fine for a while
No unexpected errors or problems seen in /Library/Logs/Console/501/console.log, or in /var/log/system.log
I've temporarily moved /Library/Preferences, /Library/Caches, and /System/Library/Caches, /User/Library/Caches, /User/Library/Preferences, /System/Extensions.kextcache and /var/db/netinfo/local.nidb to make sure none of those were corrupted (plus checked preferences with plutil), nothing fixed.
I've double checked the permissions of the root directory.
This problem did not follow an update or installation of any kind. The computer just completely locked up in the middle of using Safari (and just typing in an edit box, nothing with much of a workload) and the blue screen hang happened upon rebooting after shutting down by holding down the power button.
Single user mode appeared to work fine, although I did get single user mode to hang when trying to back up a few GB of files onto a thumbdrive after copying about 90% of the files. And then a new problem came up where afterward, now the blue screen pops up and hangs about 30 seconds after running /etc/rc returns to the prompt (and about 20 seconds after last of it finishes outputting). I've tried clearing caches again but /etc/rc still causes this.
I was going to try to run AppleJack (recommended for checking permissions and clearing caches) after copying the files to the thumbdrive, but of course didn't think to install that until after I had a problem. And now that /etc/rc causes a problem, I don't know how to attach the AppleJack .dmg file other than hdiutil, which needs the /etc/rc to have been run, and also can't remount the thumbdrive to copy any more files over.
After this recent problem, I noticed that now booting from the OS CD goes to the blue screen too and no further. Has anyone else seen such a problem? I've heard of some issues with loose GPUs in the iBook G4, but they seem to mention scrambled or no/black video (video looks fine in single user mode and in open firmware, and up to the blue screen which is clear and bright). So now I don't seem to have an option to try an Archive & Install of the OS (which I was hoping to avoid, due to effort needed to reinstall other software).

Answer 1

Thank you, I had forgotten about target mode. I was able to back up all of my files. I also copied some additional 50 GB of files of the disk as a stress test and the hard drive worked fine and quick (and because it was quicker than retrieving the same files from a network drive to my desktop).
I was hoping to also unpack the Applejack files on my desktop and put them back so I could run them in single user mode without running /etc/rc. However I haven't been able to get my Linux desktop to mount the iBook in Read-Write instead of Read-Only yet (I don't have access to another Mac at the moment).