Puzzling Problems -- Pulling Hair

So many things are going wrong, I'm not sure where's the best place to
start asking for help. Bear with me:

This past summer I built a new system:

Motherboard: ASUS P5K DELUXE/WIFI-AP LGA 775 Intel P35 ATX
Processor: Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache
LGA 775
Memory: Crucial 2GB kit (1GBx2), Ballistix 240-pin DIMM, DDR2
Video Card: SAPPHIRE 100210L Radeon HD 2600XT 256MB 128-bit GDDR4 PCI
Express x16
Power Supply: PC Power and Cooling ULTRA-QUIET PSU: SILENCER(R) 610
Video capture: ATI VisionTek TV Wonder PCI Express (added within the
past month)
Storage: Four 500 gigabyte hard drives -- three Western Digital and
one Maxtor.

I'm running a triple-boot configuration with these OSs in separate
partitions on a single 500 gigabyte drive:

C: WinXP
D: Vista
E: WinXP testbed (a small partition where I try out things before
installing them on C:)

Until recently everything's been working just great. Then two or
three weeks ago I began to get an error message at WinXP shutdown.
Something like "The instruction at 0x66903f88 the memory could not be
written at 0x66903f88" along with a critical stop sound. Didn't
happen all the time at shutdown, but pretty often. Then a few days
ago I was online and I heard a "click" and the system rebooted. Right
out of nowhere. Then, when XP loaded again, I saw this error:
"Catalyst control center monitoring program has encountered a problem
and needs to close." When I closed that window, I saw this message:
"Catalyst control center host application has encountered a problem
and needs to close."

Weird. So I decided to try Vista, which I seldom do anymore since
first playing with it, because XP is just easier to use and more of my
software works with it. But when Vista loaded, my beautiful Dreamscene
desktop waterfall appeared for a second and then the desktop went to
black. And then I got an error message saying Windows Explorer had
stopped working. Then another message saying Windows Explorer was
restarting. Then another message saying it had stopped working. And
on and on. I also got a message saying I had no ATI drivers. I also
found the Aero scheme wasn't available to load.

Weird. But I had a backup of the Vista partition, so I started Ghost
from the WinXP testbed partition and tried to put a known working
version of the Vista partition in place. Ghost failed. Now this was
getting really strange. I'd done this before several times with no
problems. So what was going on?

I noticed that the Vista partition had lost its D: drive designation.
So I used the drive manager to give the partition its D: back and I
reformatted it. Then I tried loading the Ghost backup of the Vista
partition and it worked. But when I ran Vista, it would load but all
the previous problems reappeared.

So I disconnected all four of my hard drives, took a perfectly good
previously used 120 gigabyte IDE hard drive out of a drawer, and
hooked it up. I partitioned it into two equal-size partitions and
loaded Windows XP onto the first. It loaded OK -- there was one
problem when it said it couldn't find a file on the WinXP disk, but
then it seemed to find it after a few tries and went on. I fully
updated WinXP online -- SP2 and everything. But it won't load
Internet Explorer 7 no matter what I try. Seems to load fine, but
then XP announces it failed to load.

Then I installed Vista on the second partition. Big failure. It
seems to have loaded properly, but when it tries to start all I ever
see are the little horizontally moving green blocks. When they close
and Vista says it's about to run for the first time, I hear a click
and the system reboots. I am offered the opportunity to start it in
safe mode, but even then, just when the Vista wallpaper is supposed to
load, the system reboots.

I've loaded the newest version of ATI's Catalyst Control Center into
the new WinXP installation. When I started WinXP to type this
message, I got the old "Catalyst control center monitoring program has
encountered a problem and needs to close" and "Catalyst control center
host application has encountered a problem and needs to close"
messages. And this, mind you, is on a FRESH installation of WinXP on
a different physical hard drive.

I've removed the TV Wonder from the system. I've removed all four 500
gigabyte hard drives from the system. And still it's flaky.

So ... I'm guessing I have a hardware problem. The power supply?
Memory? Or, what I think is the likely culprit, the Radeon video card

Ideas, anyone? I hate to go over to Best Buy to get a new video card,
but I may just give it a shot. BTW, the first time I tried to type
this message, the computer rebooted and I lost what I'd typed. Very
annoying. Help, please.

Bill Anderson

I am the Mighty Favog
If you want to send a private email, pls use billanderson601@xxxxxxxxx