Visual artifacts with new AGP 8x card?

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

A month or so ago, my ATI Radeon 9700 card fatally crashed in the
middle of a gaming session. The screen filled with random-colored
flickering pixels. When I rebooted, the screen had random visual
artifacts all over, both in text mode as well as in Windows. I swapped
in my old Geforce 4 Ti 4200 and things worked perfectly. Figuring it
was a cooling problem, I tried with a new fan, but this did not work
either. The ATI card showed the same visual artifacts in another
computer, so I concluded that there was a problem with the card and
that I needed a new one.

Today I (finally) received my replacement card, an Nvidia Geforce 5900
XT. To my dismay, upon plugging in the card into my computer, the same
visual artifacts appeared (purplish big pixels in regular arrays or
lines across the screen) when I booted the computer again. Argh.
Something is definitely wrong, and I can't for my life figure out
why.

If anyone has any advice to offer in this regard, I would be most
grateful.

Random thoughts:
1. My PSU has a 300W output, could this be the problem?
2. My BIOS is revision F5 when revision F13 exists (for GA-7VAX mobos,
I can't seem to find my GA-7VAXFS card on the Gigabyte website). Will
this be a factor?
3. Could this have anything to do with the Geforce 4 being an AGP 4x
card, whereas my new card is AGP 8x? The GA-7VAXFS card supposedly has
AGP 8x support, but maybe I need to upgrade my BIOS? (I am a bit
reluctant due to the fact that I cannot seem to find my exact mobo and
thus I am not sure about flashing the BIOS.)

Computer setup: (Please tell me if I
missed something.)
AMD Athlon(tm) XP 3000+
Front Side Bus Frequency 166.6 MHz
Bus Speed 333.3 MHz
Motherboard model GA-7VAXFS,
BIOS vendor Award Software International, Inc.
BIOS revision F5
BIOS release date 01/09/2003
Chipset VIA KT400 (VT8377) rev. 0
Southbridge VIA VT8235 rev. 0
RAM Type DDR-SDRAM
RAM Size 1024 Mb
RAM Frequency 333.3 MHz