If you look at the shape of a graph of failure rate of electronics against time, it has what is called a bathtub shape. It rises to a peak very quickly, drops away very quickly, stays low for a while and then slowly increases. Really faulty components fail very quickly and then others slowly fail over time. It is easily possible to measure average life times but impossible to predict how long any individual component may last.
It is possible that a component on either your motherboard or your graphics card failed and that failure led to the failure of a borderline component of the other. Without thoroughly testing both of them, it is unlikely that you will eve3r determine what component failed.