Apparently broken G5 iMac.

Question

Folks:
Got it a few weeks ago, made no additions to hardware, downloaded a few widgets and games, an EPSON scanner driver, installed Halo (the game), almost nothing else. Everything normal until two days ago. (It's a great machine for Halo!) Did some scans, downloaded some Halo mods. Suddenly machine got loggy, like some process hogging the CPU. No obvious reason, no obvious fix, so rebooted.
Now the machine won't boot, goes through the Apple logo - grey screen and hangs at a bright blue screen. Sometimes mouse-pointer control works, sometimes not.
Tried complete disk wipe and re-install OS-X multiple times. Tried resetting PRAM and then wipe and re-install. Tried all suggestions (except restting the power management unit) in Apple tech article 106464 "Your Mac won't start up in MacOS X" and the relevant articles it references.
No standard test or diagnostic indicates any problem, nor is there any error message displayed at any time. Starting up in verbose mode (cmd-v) results in a string of hard-to-decipher messages, none of them obviously alarming, and then the usual blue-screen hang.
Held down option key on boot from disti CDROM, ran Apple Hardware Test, "Extended" option.
The machine will reliably boot up in "Safe Mode" (tech article 107392). Connects to LAN in this mode, so I recovered what little data I had to another machine before doing first wipe and clean install. Seems to do everything I try in Safe Mode except running Marble Blast, which blinks the screen and then crashes.
Anything further I can do before I go back to Apple and say "It's broken"?
Thanks,
Henry

Answer 1

I'm not at all surprised that partitioning and unpartitioning and writing zeroes to the disk had no effect. Looks like the product specialist is hunting around for ideas. Like you originally said, there would never be any need to write zeros to correct a corrupted disk - once the disk is formatted again the disk couldn't care less about the previous content on the disk. After all, why would an old "zero" be less confusing to the disk than an old "one"? Makes no sense at all. Writing zeros is simply a way of securely deleting data.
This does not sound like a software problem - particularly given that it occured out of the blue, and a complete reinstall made no difference. It has the classic symptons of a hardware problem. However, it could be almost anything. But, given the atrocious reliability of the capacitors on the iMac mainboard I wouldn't be surprised if you find one or more bulging or leaking capacitors if you take the back off your machine. The symptons you describe are similar to those people with that problem suffer from. I had this very problem and had my machine replaced as it was the fourth major failure in as many months. If this is your first failure, you'll probably just get a new motherboard out of Apple.