Not sure if you solved the issue already. But in case for other people who are facing the same problem, my experience might help.
I have faced the exactly same problem on the same device. But I have solved the issue myself. What you need to do is: (1) disconnect and connect all ribbon connectors which are located under the touch pad. You have to make sure that these are connected properly and the one that connects with motherboard; (2) when you putting back all screws which are located at the backside of pc make sure that they are a bit loose (not so tight).
Note: Exception is: screws that connect hard disk, optical drive (and 3 screws below), 3 large screws and 1 small screw located under the battery should be tight. But all other backside screws of pc should be loose (not so loose that they fall easily).
To make sure how loose/tightness work for your pc, you may start your pc after putting hard disk, optical drive and battery and then put screws while your pc in on. While putting these screws you may check your touch pad to see how loose the screws should be. While putting a screw check touch pad, if you see it is not working make the screw loose until touch pad works. Do this procedure for all other screws that I mentioned to be loose. Hope this helps.