Hey, its a common issue.
Uninstall all previous graphics drivers and any software that came with it.
Then, use Drivesweeper or something to make sure there arent any redudndant problems.
Then insert the CD that came with your card, or simply download the latest drivers from ATI website and install that.
Download Catalyst ssofrtware from Sapphire/ATI and in the overclock tab make xsure you set fan profile to 100%. During gameplay, monitor your GPU temperature to make sure it does not exceed 60-70C.