well the slow CPU doesn't help. But should still get more than 10 fps. i suspect overheating first of. Get HWmonitor to monitor temps, it records the minimum and maximum, so load it up, play a game till the FPS drops, and go back and look at the maximum temps for cpu and gpu. And also you might be running things with higher detail than what your rig can handle, turn down some detail/texture/AA settings. When video card vram fills up you will get sudden fps drops like that too.