I’ve been experiencing some issues recently with the TouchPad on my ASUS mini-book. Shortly after logging in, the touchpad would cease to function. Key presses were still recognized, and the touch-screen still allowed interaction, but the touchpad itself was completely unresponsive. Restarting or logging out and back in would fix the touchpad, but only for a few minutes.
It turns out that I was the cause of my own problem. The F9 key has a sub-function mapped that will disable the touchpad. I must have accidentally pressed it when aiming for the F10 mute function at some point. That left only the question of why the touchpad would work for a short while then begin failing. The answer lies in how the additional function keys are implemented.
Since these additional functions are software managed, the ASUS library responsible for maintaining their state must be loaded before their behaviors are realized. After logging in, the touchpad would function for the couple of minutes it took the ASUS software to load. It would then disable the touchpad as I had (erroneously) requested.
If your ASUS X200CA touchpad ceases to function unexpectedly, press [fn] + [f9] to see if that fixes it.