my macbook pro keeps freezing. it's unibody. the first generation unibody. i've already had the logic board replaced on this once. any idea what could be causing this? the mouse and everything just goes non-responsive. i close the laptop and put it into sleep mode and than open it back up and it works a little big, seems really spazzy. as if all the commands i did while it was frozen all happen at once. the screen went black one time. (brightness went all the way down.) not sure what's going on, this isn't the first time it's happened either.