This is your motherboard righ? : http://www.gigabyte.com/products/pro...px?pid=3894#sp
You got all latest drivers from there?
I've had some problems with my RAM sometimes, it acctually made the system slower. But now its fine. I didnt even do anything, only a fresh install of windows. But try updating every single one of the MotherBoard Drivers and see if there is any difference. It could allso be the ATi drivers, they are pretty crap.
Yesterday I could play any game I wanted and today I cant play Valve games, just TF2 :'D