Maybe you changed your input profile in the launcher dialog ? It could happen for example if you played with a joystick, so you selected a joystick profile previously… then when you tried again later on, you had the joystick plugged out but you still ran the game with the joystick profile, instead of switching back to a keyboard+mouse profile.
Another possibility is that the window does not have focus. Could happen by accident if you al-tabbed while it was loading, but when it asked for a key to continue, forgot to move back the mouse and left-click to the focus the window. In this case, all inputs would get ignored until the game window has the focus back.