Videocard problem?...or cpu?

Hi. Ive just purchased a new PC from overclockers with the following specs…

AMD Athlon 64 4000 San Diego (Socket 939) Dual DDR400 CPU

  • AMD Freezer 64 Pro Approved Cooler
  • Asus A8N-SLi Premium (Socket 939) PCI-Express Motherboard
  • 2GB (2x1GB) DDR PC4000 Dual Channel Kit
  • 250GB Western Digital Caviar SE16 16mb cache SATA-2 Hard Drive
  • NVIDIA GeForce 7900 GTX 512MB DDR3 PCI-Express Graphics Card
  • NEC ND4570 16x16 DVD±RW Dual Layer ReWriter
  • Onboard Sound
  • Tagan TG600-U25 600W Dual Engine ATX2.01 SLi Compliant Silent PSU
  • Windows XP Homel pre-installed with License and CD supplied

Everything was fine for a week, and then I purchased a 19 inch tft monitor. Once again, everything ok for 2 days, and then games just stared to crash. The graphics would just freeze and then the screen would go black and freeze up. So i ran 3Dmark06 and the program would get all messed up after the cpu test, during the final two graphics tests. The graphics card I have is a leadtek winfast PX7900 GTX. I have just gone back to my original monitor and the problem still persists. Does this sound like a driver related issue, or a hardware fault? Any help appreciated

Check for adequate system cooling.
Try a different video card(from a friend’s comp) and see what happens.
Try a different CPU and see what happens.
Try upgrading/changing the drivers if possible
Try flashing the motherboard and video card BIOSes

If you’ve tried different vid cards AND different cpus, then the problem is probably in the mobo.