This is a weird issue in Mint Ubuntu gnome that I've only seen on one system. It may happen in your terminal or your browser but one program will just refuse to allow input from the keyboard. I am not sure if it's some weird fluke on a strange keyboard by perhaps accidentally hitting a weird key combination.
In some windows the keyboard gets weird and only / and Esc seem to work.
/ brings up quick find and sometimes Esc will close it........