There have been several times where my MacBook Air’s trackpad wouldn’t work. I tried using the keyboard to get to system preferences, search through lots of message boards to find the fix. What I discovered over many hours of research and headache is that the problem was me. Turns out the Apple Magic Mouse which sits inside my messenger bag in my office was the culprit. Somehow, the Magic Mouse was turned on. Bluetooth rules connect to it and left my trackpad dead. All I had to do was turn off my Magic Mouse and Viola! Trackpad is back to life.
If you have experienced this, try turning off Bluetooth on your Mac to determine if you had the same problem as I did. Nine times out of ten, it’s simple. Hope this helps.