XP or Vista? If it's XP go to the login screen and press CTRL + ALT + DELETE + DELETE and you'll be presented with a different style login box, type administrator, and leave the password field blank, XP by default does not have an administrator password, you can do anything as admin. Delete your mom's password and set an admin password that they can't guess. If it's Vista, do as Gourav suggested. IDK if this works for Vista, or if it sets an admin password, I think it does.