I would have to go with a loose connection theory on this one. Could also be that you have a bad cable connecting the trackpad to the laptop motherboard. Either way, it's something that you should make Lenovo's problem to fix if the unit's still under warranty, because the fix is going to involve opening the unit up.
I have recurring mousepad problems which began when I initially set up the machine. At the time I reinstalled the driver, which had no effect; however, the device subsequently began to work. After a few weeks it abruptly stopped working. Then it started working again. This morning it abruptly stopped. When the mousepad does not work, a USB mouse always does.