Dead Compaq SR2037X, sorta.

My sister recently shipped me a nonfunctioning Compaq SR2037X desktop
thinking maybe I could get it working again since I've been in computers
since the 1980's. She's already sent it to a tech guy who replaced
various components including the motherboard and CPU and yet it still
won't go. Here's what I've done so far.

I do get a bootup screen and can run around in BIOS just fine.

At first I thought it was just some loose cables since the power supply
cable to the SATA drive had come off. Hooked it back on. NTLDR is
missing. No biggie there, I was planning to install PCBSD on it
anyway.

I put the installation DVD in, and...it keeps hanging on various spots
in the kernel loading process. Just freezes solid. So okay, I'l try
the second option, installing Ubuntu 10.4 on it.

Only that DVD won't work either. I've tried both on other systems and
they work just fine, so I know it isn't the media causing this.

For the heck of it, I tried downgrading to Ubuntu 9.04. That installed
flawlessly from the CD. Very interesting. I upgraded it to 9.10. That
worked too. But when I tried to upgrade to 10.4 over the internet, it
hung up again. I feel like there's a clue in there somewhere, but
exactly what it's pointing to, I don't know.

Next up from the 9.04 CD I ran both a hard drive and a memory test.
Hard drive tested okay. Now the kicker is this desktop has two memory
modules. If I remove one, then test the other, that works fine. The
module and slot don't seem to matter. If I put them both in there, the
test starts showing errors after about the fourth time through. This
seems like another clue, as if a memory handler can't do its job right.

Now what could it be? I wonder about the power supply thinking maybe
something's getting too hot and failing in there or sending an erratic
or incorrect voltage. Unfortunately I have no VOM meter to test this
theory, and even if I did I don't know the specs, though I'm sure I
could find them somewhere.

So, what do you think? Anyone encounter a problem like this before?