My laptop's keyboard stopped working - how do I fix it?

I suspended my Aspire E 15 laptop (Ubuntu 18.04) for a couple of hours and when I switched it on its own keyboard wasn't working.

Then, when I plugg in a USB keyboard (which I'm now using to type this question), it does work.

The touchpad seems to work, as well as the keyboard's power on button.

I tried to rebbot it, update drivers and so on, and nothing worked.

What can I do?