Will not boot to CD, HDD, or boot options

I have a friend who gave me his iBook G4 to fix. Thinking I could fix this with no problem, since I had fixed MANY other Macs before and since I have extensive computer repair experience I said I would do it.

This computer has had no end of problems. At first, I determined I could not boot to a CD effectively since none of my normal diagnostic CDs designed for PowerPC were booting. I attempted formatting the drive and then loading a version of Mac OS X Tiger, and that almost worked. I say almost worked because midway through the install, the computer shut itself off for no reason. I diagnosed the hard drive and found it to be a good hard drive (using many tools over the course of this). I sold him on buying a new CD drive. Did that, and the computer still would not boot to a CD.

It should be noted that at this point the computer progressively got worse at attempting to boot any CDs. I formatted the drive multiple times with an Apple Partition Map, sometimes I even blanked out the drive with all 0s just to see if it would boot. Sometimes it would, and sometimes it wouldn't. After blanking the drive, I was able to get TechTool Pro to run, but only for a limited time before the computer froze. I determined it must be the logic board, so I ordered a new one. After a couple of misplaced orders and shipping snafus, I finally got my hands on a logic board that supposedly was used, had been tested, and was 100% working. It came with the frame and everything, so I simply unplugged the LCD and other parts from the logic board that I thought wasn't working, and plugged everything back in to the new one. The computer turned on and allowed me to see boot options.

However, now I could not get any of the boot options to actually boot. The CD drive reads the CDs fine in the boot options menu. So I decided it must be the hard drive cable. So I ordered and replaced that too.

Basically, I have now replaced the CD drive, the logic board/frame/heatsink, and now the HDD cable. After I installed the new HDD cable there was no change. I thought there MUST be something else wrong, but I had no idea what.

As what I thought would be a last ditch effort, I reformatted the hard drive again with 2 partitions, one on the back end of the drive to hold the Tiger OS X DVD installer. After I imaged that over using Disk Utility on another working Mac, I put the HDD back in. It sees the HDD image, so I try to boot from it. No dice.

At this point, any attempts to boot resulted in a blank blue screen, or the apple logo with rotating wait symbol underneath (that would occasionally freeze, but sometimes it would just keep going). Each time I attempted a boot I waited at least 10 minutes before deciding nothing would happen.

So I tried the following:

-Reset the NVRAM via Open Firmware (Command Option O F, reset-nvram, reset-all). Did that, no change.

-Reset PRAM (Command Option P R). Waited for second chime, then restarted again and pressed and held Option to get the boot menu. Now NOTHING happens.

-Try to load Open Firmware again. Now will not accept keyboard input.

-Try to reset PRAM again. Still no ability to access Open Firmware keyboard input.

-Try reset PMU per Apple instructions, now every time I turn it on, I get either a blank screen or a discolored one, regardless of whether I press Alt. Sometimes Red, sometimes Green, Sometimes just a horizontal line of white at the top with the rest black.

So now what do I do? The old logic board is taken apart now and is unlikely to be used again, and I can't imagine my tinkering around is irreversible with simple NVRAM and PRAM and PMU settings. There has to be SOME way to figure this out. I throw myself on the mercy of the experts.

UPDATE: After leaving it off for a while, it seems to be able to get to the boot option screen again, but still won't boot any of the options.