Ubuntu 14.04 Login screen password always incorrect

I have just installed Ubuntu 14.04 for the first time boot. I am a long time MS Windows user and don't like where Windows is headed so I decided to switch to Ubuntu and only use Windows for gaming.

However. I cannot get into my computer after the lock screen appears. It says the invalid password message no matter what password I use.

I have googled for a little bit, and the closest thing on here I could find is: Password is incorrect - when tried to login into Ubuntu 13.04 [duplicate] . Though there is no answer there.

I should note, that I mistakenly as a Linux newbie:

• Did chown -R david /etc and lost the sudo power.
• then I booted into recovery mode and ran a few things and ran chown -R root:root /etc and that fixed the sudo problem. But I think when I did that the lock screen stopped working and I can't get into the computer. I have to restart and have it auto login.

I went through the first 10 suggestions when posting this and nothing close helped.

I had this exact issue. The password worked in terminal, but not in LightDM. I could login as other users, just not the one I wanted. I even changed the password from a different user and also in recovery mode. LightDM didn't give a password incorrect notice, there was just a graphical glitch.

I don't have a fix for LightDM, but this works for me as a work-around, I set GDM as default display manager - GDM is not having any login issues:

• Install GDM.

  sudo apt-get install gdm
  

  It will ask you which display manager to set it as Default, select GDM.

• If it is already installed. Run reconfigure.

  sudo dpkg-reconfigure gdm
  

Reference: How To Switch Between GDM And LightDM In Ubuntu 14.04 [Quick Tip]

I encountered the same on the lock screen, and found out that my account was suddenly locked.

I'm using Ubuntu 14.04.1 (lsb_release -a). I installed the latest update and then encountered the issue, password is incorrect when the screen locked.

So I googled and saw that from most of the suggestions, one is to change password.

I found out that the only account (admin account) I'm using was locked. So I unlocked it and I'm now back in.