Logged out of computer & can't log back in with correct password

I never log out of my macbook pro computer. But for some reason it kicked me out of my login and made me type my password. So I did, and I put in the correct pass word but then it just stays there a loads forever. I try different passwords and it just freaks out. So when I put in the correct one it just doesn't recognize it for some reason? What can I do to fix it? Can I fix it so I can get onto my computer? I have also tried shutting it down and restarting it to see if that would work and it didnt.

Boot off your Mac OS X DVD and use the built in tools to reset your password on your Mac.