Is there a way to change that password? Are you logging in as you (not another user)? If you continue to have problems, I would ask you to do (1) a new install, or (2) try to create a different account so you can change the password of the original, however I do not think the second one is possible because I can only guess you do not know the root privileges. Normally this is way Ubuntu (and more than likely Kubuntu) is set up (which you can read more about this here
I don't exactly know much about Ubuntu (or Kubuntu), but I think to the sounds of it you can only do a fresh install, or find a work around. You have not had the install that long, so there is nothing wrong on doing a fresh (fresh) install. If I am correct, you don't have root access, so I can't ask you to change the password.
Hope this helps, but if it doesn't, leave another reply!