mambonike

i have g-force xfx 5500 nad i have a realy big bad something here when i play any game any type the graphic begain coool and good and begain 2 be bad and slow and then be normal and then slow again so what i can do by the way when i buy the card it worked so good and nothing of this happend i have 512 DDR prossoer 2.6 cash 265