Murphy's Law: No startup after slew of problems.

Question

Hi. I'd like to thank everyone for reading this in advance, because I'm in a bit of a pickle if I can't get this machine functioning.
Short Version: After a system-wide freeze while using Final Cut Express on my PowerMac 1.8 GHz, and assorted glitches upon restarts, the computer is no longer completing the startup process - No startup sound, visual feedback, nor much of anything else save a brief warm-up sound with the fans. Do I go into the Apple Store and get some work done, or is there a DIY solution?
Long Version (What you need to know): This is an Apple Store refurbished PowerMac Dual 1.8. It came with 1 GB of RAM, ATI Radeon 9600, 160 GB Hard Drive. Since purchase, I installed a Radeon 9800, and have two external hard drives active, a 160 GB (FW 400) and a 300 GB (USB 2.0).
About two weeks ago, I purchased an external hard drive kit for the 300 GB drive. A week ago, not necessarily to the day, I had a previously unseen kernel panic. As I haven't had one since the days of X.3, this was a rather uncomfortable incident, but as it did not repeat, I presumed it was just a random glitch. I repaired permissions on all drives, and presumed the situation was resolved.
Today, I was doing a significant amount of editing with Final Cut Express. By significant, I mean 8 hours plus of footage (A bad idea, yes, but I was in the process of removing a good portion of it). Other than intermittent checks of NetNewsWire and World of Warcraft, things seemed to be functioning properly, as I was waiting for the waveforms to render for the DV. About 4 PM, Final Cut began acting strangely. Footage did not adjust properly, sound files would lag, and I became concerned.
Eventually, I saved and attempted a force quit, which only served to make things worse. As I right clicked on the program icon, the entire computer froze completely (aside from the mouse, nothing was responsive), and I did a forced shut down. I turned the computer back on, but it stopped at the gray Apple screen that often arrives at startup. After a few minutes, every fan on the computer was whirling at full speed, and in fear of the safety of the computer, I did a force shut down again.
This time, the desktop appeared, and all seemed well. I went into Disk Utility to see if something was directly wrong. As it verified the drive, I also turned Final Cut back on, but Express glitched upon opening, and the launch window's text turned white. As it was no longer responding to force quits, I did a forced restart again. From there, it repeated the first incident two more times. The gray Apple screen, the fan wind tunnel, and the lack of desktop.
I decided to let it cool down for a little bit in hopes it was a heat issue. After letting it sit for about a half hour, I turned the G5 back on. This time, I received nothing in response. All fans responded, the ATI 9800 whirred on full, and- stopped. The process stopped upon reaching the point where the startup sound typically would be. Although the video card kept whirring, everything else stopped. I then removed all non-essential peripherals, save monitor, keyboard/mouse, and Ethernet connection, to the same results.
In frustration, I attempted a Plan B. Opening the side of the case, I cleaned all components I could get my hands on, and swapped out the newer 9800 for the 9600, thinking the lack of display was a video issue. This was not the case, as even after my swap, the computer failed to respond. I repeated this with various connections, plugs, rooms of the house, so on and so forth, to no avail.
The question is, is there some solution I'm missing as far as getting this to operate properly, or should I just hedge my bets and take it to the NMA Apple Store in Chicago? Your advice is GREATLY appreciated, as the sooner I can get this to work again, the more time I have to work on this considerable Final Cut assignment.
Thanks in advance,
Agnate
PowerMac Dual 1.8 GHz   Mac OS X (10.4.6)  

Answer 1

You can try a NVRAM reset, which often helps with firewire related issues:
Steps to reset nvram :
Power Down
Hold down Cmd-Opt-O-F
Power On
at Open Firmware prompt, type:
reset-nvram
reset-all (this just reboots)
If you can't get this far:
Try to boot off the install DVD. If you can then...
Check your hardware using the hardware test disk that came with your system. (Sometimes this is included on the install, or recover disk).
If you just keep getting nothing, it's time for the apple store