Graphics Card Problem: Hardware or Driver Issue

Dear All

I’m experiencing a serious and so far unsolvable graphics card problem.
Screenshot:
1024x768: http://www.redfernonline.com/nvidi [...] en_big.jpg
640x480: http://www.redfernonline.com/nvidia/corrupt_screen.jpg

This issue only started occurring when I did a complete re-install of windows. Not only does the screen image display these corruptions but the system shows and the signal to the monitor is intermittent. A driver clean then re-install can sometimes solve the issue but not permanently. Sometimes things are fine for days, in one case even weeks, but the issue always recurs. The display appears to be fine when Windows is operating in safe mode.

I have tried:

Re-installing display drivers
Re-installing older versions of display drivers
Using Driver Cleaner then re-installing drivers & older versions of drivers

Its not a monitor problem. My Dell 1905FP works perfectly as an extra monitor for my laptop.

I don’t think its a power problem as I have tried booting up with 2 HDDs unplugged and the power to the sound card unplugged.

Its not a compatibility issue as the card has worked perfectly with the motherboard for over a year.

The card is a passively cooled nVidia 6800 from Gigabyte (GV-N68128DH - http://www.giga-byte.co.uk/Product [...] ctID=1198)

The rest of the system is as follows:

Mobo: Leadtek K7NCR18D ProII
CPU: Athlon XP2800
RAM: 1024Mb, 2x 512Mb
Power Supply: Antec 380 Watt True Power
SATA Card: Adaptec 1210SA (Raptor Attached)
HDD1: Western Digital Raptor 36Gb (System Drive)
HDD2: Western Digital Caviar SE16 250GB 2500KS SATA
HDD3: Maxtor DiamondMax Plus9 160GB 6Y160M0 SATA
Sound: Creative Sound Blaster Audigy 2 ZS Platinum Pro (with external box)

I look forward to your help.

Cheers
Jonny