Yeah, OK. I found this possible solution. It may be a keyboard message popup problem:
Edit: even though it looks like you are using a desktop PC not a laptop, check that you don't have any utilities running that might be intercepting your keyboard presses or trying to display popup messages. Also, try disabling the Steam overlay and any graphics card overlays. Also, you could try switching between fullscreen mode, windowed mode and borderless window mode to see if it makes any difference.