over heating most likely .
those old gf mx cards usually start video tearing when they get to hot . Cpu overheat is usually the shutdown ,or worn out circuits .
clean out all your fans, heatsinks, air intakes , ram ,ect .
start your pc and go to the bios (del key) now check your hardware/system monitor in there . note the cpu and case temp . let it warm up , if your above 50c cpu temp then your gonna have problems running games . you may need to clean and reapply artic silver to the cpu heatsink .