Need Methods for Testing Hardware -- Dual 2.0 GHz Won't Boot

Question

Have a Dual 2.0GHz Power Mac (M9032LL/A) that won't boot.... I'd like to know how hardware is diagnosed on these machines? I hear the Apple Hardware Test CD isn't that accurate and not really any help and there's no LED lights on the logicboard of these models, so, short of swapping stuff out, how do I tell what's bad? I'm assuming either a processor, the logic board, or maybe the video card are bad and would like to verify what may be wrong.
The computer doesn't boot reliably but once it is on, it works great. When the power button is pressed, there's no chime, but it makes the other usual appropriate noises, such as the fans and hard drive briefly kicking up and back down... then no more progress. The mouse never lights up (it's optical and flashes when the computer starts up normally), no video ever shows, and the computer just sounds like it's sitting idle-- the fans are slightly on, but the hard drive makes no noise. After several minutes, the fans begin to go into overdrive (the wind-tunnel sound) and I just have to shut it off with the power button.
This problem has become increasingly more bothersome over time-- it used to happen only occasionally. Now the computer won't start on its own at all. Booting into open firmware has tricked it into booting, but has become less and less reliable (described below).
+For those that may be able to help further than recommending hardware testing methods, here's specifics on my situation:+
Troubleshooting I've done:
- reset the PMU (can't remember if I've reset the PRAM)
- installed a new power supply
- tried a different monitor and power cord
- installed a new battery
- re-seated video card
- removed the two sticks of third party RAM... when I booted after doing this, the boot got further. This time the computer acted like it was on, but with no video... it responded to the keyboard (volume and eject) and appeared to show up on the network. I checked monitor by plugging it into laptop, and the monitor worked fine, so I assumed the computer's not outputting any video. Force-shut-down and rebooted the computer, but it went back to the same boot problem described above (fans went into overdrive).
In the past I have successfully booted it by booting into open firmware, then typed 'mac-boot' and the computer starts up and works completely fine. It's not flakey, doesn't crash, etc. However, it won't reliably boot into open firmware!
I've also successfully booted into single-user mode. Both in this mode and in open firmware, the fans will go into wind-tunnel mode after about the several minutes as it does when booting via power button alone. However, the command line is still responsive, and a boot command stops the wind-tunnel noise as the computer then boots.
I'd really like to rescue this computer, it's such a speedy, reliable machine that's given me years of excellent performance. If it's time to let it go, I'd like to know for sure, so a way to test the hardware, especially the logicboard and processors, would be nice...
Many thanks for any help,
Selena M.

Answer 1

To those that offered help, thanks, I appreciate it and ended up finding the problem using the most basic hardware test of all-- remove one of the parts on the suspect list, so long as the computer can run with out it, and see what happens, and that resolved my issue!
To those having the same problem-- I found a fix for my machine and it's working great!!! The primary suspects were: logic board, RAM, CPUS or video card. If it was the logic board or a CPU, I'd just call it a parts machine, so tried removing the other parts to see what happened. Still crashed/didn't boot without the third party RAM, and also no difference without the Apple RAM.... but when I removed the video card and hit the power button-- there was that startup chime I hadn't heard in so long!!!!! The machine booted immediately and responded properly to the keyboard's volume and eject buttons. Since I couldn't attach a monitor, I accessed it over the network and it was working fine. I shut down and booted several more times, and it came on every time. So, if those of you that are having the same problems haven't tried this, see if your computer boots without the video card...
*Best of all*, the new video card was free! Apparently the card in my machine has known issues and they'll replace it for free if you send them your old one AND mention this article: http://docs.info.apple.com/article.html?artnum=32473. Read through it, and if your video card matches that model number they list, call the phone number they provide. Make sure you mention the article number, which is 32473, so they can reference it and so they won't charge you an over the phone tech support fee (because this is for a recall). They'll look the article up, ask you what you did and so on. Tell them you tried everything the article suggested and that your computer behaves as the article describes, and they'll send a new card.
Also, note that I'd seen this article before when trying to solve my booting issue, but my computer didn't behave exactly like they described, so I just kinda blew it off. But later, while skimming various forums for answers, I read a post from someone with similar booting problem to mine and he offered the above tip and article number. It's a good thing too, as it saved me the cost of a video card! Otherwise, I just would have bought a new one.
Anyways, I hope this can help one of you out that are having similar problems... just remove that video card (if you haven't already) and see if your computer works. If so, get a new one for free from Apple and hopefully you'll have your computer back!
Good luck!