hey guys my graphic card is nvidia geforce gtx 550 Ti amp and its casing is manufactured by zotac. When i play call of duty black ops on 1920 x 1080. My pc get off within 20 minutes. while playing game i checked the temperature of my card after 10 min it was 74 C. what should i do. should i make some changes in pcie frequency or what should i do. i have 120mm fan installed in my pc case.