Small,
Hardware side :
Can you tell us what motherboard you are using and also which PCI-e slot you are using on there for the graphics card?
Can you also tell us what model of power supply you have and how many watts?
Windows side :
After you did the clean boot, did you install any 3rd party graphics apps (ie : Afterburner or Asus) or did you just install drivers and try to run a game?
Are you running the drivers that came with the card or downloaded through windows/website?