Mac Pro Restart and Hardware Test Problems

Question

This appears to be a continuation of a thread I began titled "MacPro Restart or Reboot Problems" in which the reboot problem still seems to be evident.
Initially, I was having problems with rebooting but after rebuilding my directory with DiskWarrior, the issue disappeared. Then recently, I entered my password and the Mac restarted itself and the same problem is back where the drive seems to try and "catch" but can't.  And now its back to  happen anytime I want to re-boot (however, this tends to be rare.)
So I ran DiskWarrior again and it reported no problems. Then I tried to run Apple Hardware Test and about 40 seconds into the test, with the message "Testing memory" stated, the fans begin to spin at a high pitch.  The system locks up and the only recourse is to press the on/off button on the front of the Mac Pro.  If I try to wait it out, the Mac Pro will scream and spin until I restart.
I've ran the same AHT test on an identical Mac Pro that is only a few months older than this one and even using the Extended test, the AHT takes a little over four minutes.  And the Testing Memory message appears early in the test  and moves on.  Then, much later in the test, the fans spin up to the same high pitch whine like the problem Mac Pro.  But only one at a time (there seem to be three of them) and each one quickly quiets down once they're tested.
So that's the beef. Something I've considered is this Mac Pro came with two Gigs of Apple memory installed. I'm wondering should I uninstall one of them and re-try the AHT to see if it could be the memory.
Any suggestions would be appreciated!  Thanks!

Answer 1

I took my G5 to an Apple Store (2 hrs away) and had a Mac Genius look at it. I told him about the reboot issue and the weird skippy sound it made when it tries to reboot. When I mentioned about the G5 locking up during an AHT, he thought that sounded like a hard ware issue. So he ran a diagnostic test with his Apple CD and the G5 tested fine (?!!) We then ran my original AHT disc that I had brought with me. It too tested fine-- it didn't lock up at all! We rebooted like a half a dozen times-- with both keyboard and via the menu-- and it rebooted like a champ. Everything we tried, the G5 rebooted fine. I asked if maybe the keyboard, mouse or monitor back in my office could be part of the the issue. He replied anything connected to the G5 could be a culprit.
So I brought it back and hooked it all back up. And it would not reboot! It tries to reboot and makes the same sound, same problem! I disconnected and replaced cables and keyboards and mice. No dice. I took the G5 down to an edit bay where we have an identical G5 (same 2 GB of memory, maybe 3 months older) and connected its power cable, mouse, keyboard and Cinema Display monitor to my G5 and tried it. No reboot, same problem. I reconnected the older G5 back to its original cables/setting and it reboots-- no problems.
I'm at a loss. I guess I will go about doing a zero drive process and see what that brings... However, one thing I have seemed to confirm: the skippy sound that continously emunates from the G5 as it attempts to reboot seems to be coming from one of the optical drives (the G5 came with two DVD optical drives). I'm wondering if I go in and disconnect the optical drive(s), will that lead to something??
BTW, I did hook up the G5 to another monitor, thinking that maybe it could be a graphics card or monitor issue with the original display. I used a PC monitor with a DVI connector and the problem was still there.