Here's the update:
I am having the same problem.
Specs:
AMD AthlonXP 3000+
Radeon 9800pro 128mb (1 month old)
Corsair twin-x 2x1gig sticks of RAM
Gigabyte 7N400-L motherboard
300W no name brand PSU
I have tried the following:
Updated the nForce2 chipset drivers, updated the BIOS, updated to CCC 6.3. Also tried Non-CCC 5.11 (Which worked for about 15 minutes but as soon as I went into the display settings the screen went black and had little red tearings on it, had to reboot it)
Virus and spyware scanned (AVGfree, Ad-aware, Spybot S&D)
AGP8x disabled
Aperture increased from 64 to 128 then to 256
Fast-writes disabled
VPU recover disabled
Took out the Audigy2ZS sound card
Took out 1 stick of RAM, therefore only having 1gig of single channel running.
Unplugged the extra HDD and both DVD drives (In case of power issue)
The molex connector was plugged into the 9800pro.
Re-attached the heatsink as it was wobbly.
Changed the AGP to 1.6V as a last resort thing to try.
My 9600pro works fine without a single problem. The 9800pro however only gets to the section of booting which is meant to display the Login screen but the monitor goes into standby as though the PC has been turned off.
It originally failed just after logging into World of Warcraft, the screen went all weird (artifacts I imagine, the g/f was playing it at the time) then had to reboot.
I've got an ATI support ticket...we'll see just how much that helps, lol. (So far they said to do what I have already done ->Update BIOS, chipset, ATI drivers)
The only other thing which I need to try is put a desk fan in front of it and see if it lasts longer. Or try the card in my brothers PC which is running a x850 so therefore would run my 9800pro.
Any help would be greatly appreciated.