I installed Windows XP on my Socket 754 PC last night, and until I ran 3DMark2001SE everything was going super smooth. Then, strangeness ensued.

First of all, the system components:

FSP 300W ATX PSU
ASUS K8V Deluxe K8T800 Motherboard
Athlon64 3200+ Clawhammer
2x256MB DDR400 RAM (System refuses to POST with other 512MB and 1GB sticks I have, in case it's related)
HIS ATI Radeon X1950 Pro AGP 512MB
Creative Audigy 2 ZS
Windows XP Pro SP3

I installed the following drivers in this order:

Via Hyperion Pro 4-in-1 5.24A
(A bunch of SATA and Network drivers)
AMD Cool n Quiet Driver
ATI Catalyst 10.2 Legacy Driver
.net Framework 2.0
.net Framweork 2.0 SP2
Creative Audigy Series Driver 2.18.0017
Creative Soundfont Manager (I do not remember the version)

At this point everything was working fine, the GPU was showing up in GPU-Z running at 8x AGP mode, the desktop was working at 1920x1080. Perfect.

I then installed:

Directx 9.0c June 2010.
3DMark2001SE
3DMark03

Then I ran 3Dmark2001SE, ran the benchmark, loading screen came up for the first test.. then a blank screen, no video signal and system hanged.

I hard reset the system, only to get to the desktop and get a brief popup window telling me that SMARTGART was doing tests to determine the optimum configuration for my graphics processor, then again, blank screen.

From then on, at every boot, after the Windows XP Loading logo I get a blank screen and no video signal.

I can start the system in safe mode or in VGA mode (via F8 at boot) and it boots just fine that way. I can't get a normal clean boot anymore, however.

Things I've tried:

Change AGP Aperture Size betwween 32/64/128MB
Enable/Disable MDA sources
Uninstall and reinstall Catalyst 10.2 (via Add/Remore Programs)

This is looking like a hairy ATI driver vs motherboard AGP implementation thing, considering it's very likely a SMARTGART failure. Things I'm considering trying:

Check system logs via safe mode (not sure how I forgot to do this..)
Set AGP Mode to 4x in BIOS (much performance hit if at all any? I remember doing this as a fix to a similar issye with a KT400 or KT600 in the day..)
Increase AGP voltage to 1.7V
Use video driver uninstaller to uninstall Catalyst 10.20 and install an earlier Catalyst (9.3? 9.11?)
uninstall Hyperion Pro drivers and install an earlier Via Hyperion Pro Driver (Which version? 5.13A?)
Install a modern 500W PSU in there just in case it's a PSU issue (but I doubt a healthy FSP 300W would not cut it for this system..)

If anyone is familiar with the issue and can help I would be very glad.