Keyboard stopped working for one user - and one user only

Since yesterday, my keyboard stopped working. I type but nothing appears in the text input. If, for example, I press "Enter" on the browser's address bar, no request will be made. The mouse works perfectly, but both my notebook's keyboard and the USB keyboard I use fail to work.

It only happens with my default user account: if I log into another account on my machine (Ubuntu 14.04 with Unity) it will work; it also works at ttys. However, if I lock my default account, the keyboard does not work at Light DM either.

Notice: it can happen on other versions of Ubuntu, either with Gnome or Unity or the default interface. Verified (!) with 20.04.

Solution 1:

This post solved the mystery: I just enabled the "Slow keys" option by mistake. It is easy to solve:

• To to the cog icon at the top right corner, choose "Settings":
• Go to "Universal Access":
• Go to the "Typing" tab.
• "Slow keys" is marked as on: Toggle it to "off".