Login screen won´t let me put in password

Hi all, When I close down the screen on my laptop (I guess it hibernates? Whatever the default is), then open it again, the login screen comes up. Sometimes it won´t let me put in my password. As if the keyboard isn´t working. The only key it picks up is the space bar (ie when I hit the space bar the hidden characters come up in the password panel). So I have to restart and then it works. It...