A shame that my first Hexus post is a plea for help, but I have just assembled the following system and unfortunately all isn't going according to plan:

Abit AB9 Pro (latest BIOS v1.5)
Intel Core 2 Duo E6600
2 x 1gb Corsair Valueselect DDR2 667
Sapphire Radeon X1950 Pro 256mb PCIe (TVO i.e. no VIVO)
Seagate 250gb 7200.10 SATA
Corsair HX520 PSU (total 40A on 12V rails)
Windows XP MCE 2005
Fujitsu Siemens S20-1W monitor, running at 1680 x 1050

The rest of my hardware is just a DVD burner, CDR/DVD combo, a floppy/media card drive and 3 system fans. Nothing is overclocked.

The system is rock solid when just running windows, and will happily play NFS Underground 2 on max settings with no fuss.

However, when I first came to run 3D Mark 2003 the system would lock up on the troll's lair test. Whenever this happens the screen goes black (powering down the monitor) and the GFX card fan speeds up to 100%. Sometimes the sound carries on playing, but eventually the PC resets itself. When it does this I get a '2b' POST error on the MB saying which means it can't load the VGA BIOS. Turning the computer off and back on again rectifies this.

I ran Memtest86 3.1 and sure enough it found some errors. Looking on the net it seemed upping the DDR voltage from 1.8 to 1.9 would help. This did the trick and 3D Mark 03 completed with a score of 17,039. All was fine until I installed 3D Mark 05. Now the system was locking up on the canyon test.

Thinking it was still the RAM I dropped the settings to Dual channel 533 Mhz at 4-4-4-12 timings, so the RAM is now running in sync with the FSB. The system now passes every MemTest86+ v1.65 test I've thrown at it, and also completed 3D Mark 2005 for the first time, scoring 10,268. Still not very happy that I've had to down-clock my RAM though.

However, the system still locks up on 3D Mark 06. I installed ATI Tool 0.25 and can replicate the same lockup with the artifacts test after about 2 minutes. The resets seem to happen when I reach 63 deg C. Playing with the fan speeds helps prolong the test a bit, but doesn't solve the problem.

Overheating at 63 deg seems unusual, and I never suffer any artifacts - the system just resets itself.

Other things I have tried (and have had no effect):
- Connecting the additional 12V molex connector on the motherboard, which provides extra power to the PCIe slots.
- Connecting the PCIe socket on the GFX card to the other output on the PSU (it has 2 PCIe outputs).
- Using Catalyst 6.9 that came with the card, and 6.11 from the Sapphire website.

I'd be surprised if this was PSU related as I've seen nothing but good reviews of that supply and it appears to meet all of the specs on the Sapphire box.

Unfortunately I don't have access to any more DDR2 RAM or PCIe graphics cards or motherboards for further trouble-shooting. The only other PSU at my disposal is a 3yr old 420W thermaltake with a 20pin ATX connector that I don't want anywhere near my new rig!

Any suggestions greatly appreciated.