Since it's always best practice to have AT LEAST two admin user accounts on a computer, you should be able to login with a different user and change the password on your account.. If that doesn't fix it, then your account may be corrupted and you can then create a new one and copy your data over to that.

If you don't have a second admin user on the computer, hopefully you have the Recovery Discs or a Recovery Partition on the computer which will allow you to run a repair install.

Hope this helps.