My wife’s Asus netbook has a Synaptics touchpad that recently stopped working shortly after each reboot (under Windows). Haven’t fixed it yet, but the work-around is to use the keyboard to navigate to the touch-pad controls in Control Panel, then manually re-enable the pad. It only takes a few key presses to do this, after which works normally until the next restart.
Why it keeps getting disabled on start up is still a mystery, but I assume it’s a software issue since the hardware works fine once re-enabled.