Did you buy from evga/xfx they offer lifetime warranty see if the manufactor can replace it. If not time for an upgrade. The 4850 is noticeable faster but i would recommend a 4870 instead since there priced similarly.http://www.newegg.com/Product/Product.aspx?Item=N82E16814131140
Whats the rest of your pc spec? cpu,ram,psu,etc??