I just purchased a new ASUS laptop. I updated to Windows 10 immediately so I could get used to everything all at once. I use a small external mouse for travelling, and the touchpad quit working the second I plugged it in. Even after I disconnected it from the USB and restarted, the touchpad still would not work. I was told this is a bug and they are working on it.
After I read through the comments here, I went to Settings, Devices, Mouse and Touchpads, Additional Mouse Options and there it was under ELAN it said it was disabled. I enabled it, and now I can use the touchpad!
Thanks!!