PPC G5-Quad panic kernel woes

My G5-Quad had a kernel panic this afternoon.

Two attempts to reboot normally eventually ended in the gray box with the well-known multilingual instructions to restart the machine, obvious signs of further kernel panics.

Two attempts at running applejack in safe mode (Command S) were aborted by the machine shortly after it started checking stuff with a message like "Release the PPC, we are hanging here".

Now it doesn't even boot in safe mode. On an occasional try, a white screen with some small black text but does not accept any commands.

Then it just wont boot. It sounds normal for a while, then the fans and pump spring into heavy action.

I opened the optical drive with the straightened heavy paper clip (only way to open it) and put the AHT test, tried holding the Option key, but the same behavior persists: no signal sent to the monitor, then it sounds normal for a while, then the fans and pump spring into heavy action again.

The first time I got the kernel panel, I was able to copy the crash report, but now I can't even get at it.

I'm working on my Mac Pro Quad right now.

I hadn't had any trouble whatsoever with the PPC G5-Quad in so long, that I've practically forgotten all about troubleshooting a PPC (getting more "senior" by the day, with brain damage caused by a series of mini strokes; diabetic type 2)

Any ideas as to what to do next? I do need Classic and a PPC CPU to run a lot of irreplaceable and indispensable software that does not run on Intel machines.

If I can't fix this machine, I'll probably be looking for an exact replica of this (July, 2006) PPC G5-Quad. Hope to move RAM and cards, etc.

2.5 GHz Power Mac (PPC) G5-Quad; 16GB RAM; mutant, flashed 550MHz nVidia GeForce 7800GTX 1,700MHz 512MB VRAM; ATTO ExpressPCI UL5D LP SCSI card; Mac OS X Tiger 10.4.11 and Leopard 10.5.8 boot drives; intrusive Spotblight, Dashboard and Time Machine permanently disabled; dual 22" CRT monitors; USB wireless 'n' available but connected to the Internet via wired Ethernet; FW flatbed scanner; 2 SCSI scanners (one tabloid-size transparency scanner and a film scanner); various internal & external HDs; FW Epson 2200 and Ethernet Samsung ML-2850ND printers; 2 X Back-UPS RS 1500 XS units.