I've just come back from a hospital appointment and had one hell of a job logging back in to my computer. It was almost as if my keymaps had been changed. Whilst at the login screen the number '0' opened the menu containing "shut down"! So I thought that I'd change my keyboard in case something had corrupted it. And lo and behold, there was a liquid puddle under the numerical keypad on the keyboard shelf! And then I remembered that I'd knocked my cup of tea before I went out and only thought that it had only a slight splash onto the keyboard, but it seems that I was wrong. So the moral of the story is -
If there is a liquid puddle under your keyboard, then consider changing it, as its very likely that there is liquid inside your keyboard!