Why can't I type my password in?

My laptop works till I reach the point where I should be able to log in. You turn it on, you see the screen, first you see the green Acer logo, the you can see that "welcome" picture with the time and date, the wi-fi and battery sign. Normally at this point I just push enter and there's supposed to appear that little user picture with the space to type in the password, but now I do and nothing besides that everything except the welcome picture disappears, it scrolls up. When I push enter again it appears again and so on. But the logging in sign just doesn't appear. How can I fix it?