Bizarre QS G4 Startup Problem - Power LED stays off, emits continuous tone

Well, I've got this really strange problem on my QS G4 that has me totally stumped and I've been searching all over the place and haven't seen anyone who had the same problem! I'm hoping someone can help me get oriented in the right direction here!

Synopsis:
At start-up, start-up tone sounds, hard drive starts spinning and then everything gets weird. No power goes to the USB ports so my keyboard and mouse don't work and the power button LED remains dark like the machine was off. Then the machine plays a continuous tone that sounds like. . . welll. . . BEEEOOOOOOOOOOOOP! It's not the series of beeps that tell you that something is screwed with your RAM or HD, etc. It's just a non-stop tone.

My System:
933/QS G4
1 Gb RAM
60 Gb IBM Deskstar + 80 Gb Maxtor DiamondMax Plus
Superdrive
OS 10.2.6
GeForce4 MX Graphics card

Details of My Ordeal:
Lately I've had frequent system freezes on my computer and then subsequent start-up problems. The system will freeze doing aboslutely innocent things like moving the mouse over a dock icon. In fact, this is the way it happened a number of times. I put the pointer over iTunes or Safari (etc) and then everything freezes.

Once my system freezes, I often won't be able to start-up my computer without zapping the PRAM first. Sometimes after I manage to start it up again, the computer is S-L-O-W like it suddenly was channeling the spirit of my old Quadra.

I thought my HD was dying so I bought a new one, which from what I understand is known for the infamous two beeps issue, but that's not the same thing as what I'm going through. The new HD seemed to help, but now I think it only delayed the inevitable.

Then the same problems started happening again. It just froze again and this time I can't get it to start-up again even after zapping the PRAM. There are two very peculiar things that happen when I try to start-up.

1) I hear the start-up tone, the hard drive starts spinning, but the power button LED doesn't light up and no power is going to my keyboard or mouse.

2) Then my Mac plays a continuous beeeeeeeeping tone that doesn't stop or break until I turn it off.

What I've tried:

- Removing my RAM to use only one of my Three PC133 DIMMs at a time

- Switching Slave and Master configs on my HDs. Using either my new or old HD in the Master config.

- Booting from an external CD-ROM drive...useless, it doesn't even try to access it.

- Replaced my PRAM battery.

--------------

I'm stumped! Does this sound familiar to anyone!

Well, I was afraid someone might say that, though I was pretty much expecting an answer like that. Anyone have any clue what a new motherboard or processor repair would cost?

Question: Assuming my motherboard or processor bit the dust, how probable would it be that it managed to start-up again once after all the problems I described above? It did manage to start-up again, but only once and it crashed shortly after login. It's been tone dead since.

Rescuing the hard drive data

Well, I've pretty much accepted that my machine is dead now and I'ven taken on the task of fetching my data from my dead machine's hard disk which is the IBM Deathstar 60. The problem is that I can't mount my old volume! Argh, Disk Utilitiy sees the old volume, but can't seem to repair it. Norton Utilities also sees the volume and wants to launch Disk Utility to repair it.

Is there a heavy duty product out there that will help me get some of my data off the drive? I've got back-ups, but also have a week's worth of intense work locked up on that *#@^#$@ thing.

Will something like Disk 10 or whatever that Micromat product is work? I'm even ready to try to initialize the hard drive using disk utility so I can use Norton Volume Recover to attempt to get some files back.

Thanks so much to everyone who's reading this. I really feel kinda bad that my first posts are these cries of help.