I have a 13-inch early 2015 Macbook Pro with Retina display, and today the keyboard and trackpad stopped working completely. (I have OS X 10.11.5 if that's relevant. I can't update to sierra, as a software I use is not compatible with it). The only thing that works is the power button. Now, this isn't unprecedented. This started happening a few weeks ago, but every time it happened, shutting down and restarting by holding the power button fixed the issue. But today it didn't.
I know there are many questions like this, but I tried every single solution I found. This probably means I won't get one here either, but I want to try this before I have to go to the Apple store.
I plugged in a USB keyboard to my laptop so that I could use it. I also plugged in a USB mouse, but that mouse plugs into the keyboard, not into the computer. Both worked fine. I tried an SMC reset and a PRAM reset, using both the built-in keyboard and the external keyboard for the required inputs, for a total of 4 attempted resets. I can't really tell if they did what they were supposed to or not, but they didn't fix my keyboard.
I booted in safe mode (using the shift key on the external keyboard. Using the one on my laptop didn't work, and it just booted normally), and the issue persisted.
The other solution I saw was to disable FileVault, but it was already disabled prior to this incident.
I also saw people saying plugging in a USB drive during login fixed the issue, but this didn't work either.
The last solution I tried was to let the computer sit while powered off and not connected to the battery. This didn't do anything either.
I did not spill anything on my computer prior to this incident, so I have no idea why it started happening. If anyone has solutions for this that I haven't tried yet, please let me know.
EDIT: I just noticed that if my computer is asleep, clicking the built in trackpad wakes it up. However, the trackpad doesn't do anything else.