does it require a molex connector to connect it to the psu if so is your psu powerfull enough I have just put a fx 5900xt in mine and i had to upgrade my psu to a good quality 500watt unit./ in your ati
settings turn vertical sync of and antialising/ of then try it if this
solves the problem hem gradually turn the setting back on(except vertical sync this really does kill frame rates)