I have been using Ubuntu 14.04 for nearly 8 months now and have been a long time Ubuntu user. Recently, I disabled the password for my user account and later re-enabled it. However, ever since doing that, I am unable to lock the Ubuntu desktop. Clicking on the Lock Screen option on the top right corner simply causes the lock screen to very faintly flash once and then nothing happens. I tried changing my password but that didn't work either. Instead, now my login passoword and my keyring password are set to be different so that every time I boot I have to type the keyring password again.I already checked the "Brightness and Lock" controls where the options is set to lock after 30s and to require a password for logging back in. Any ideas on how I could fix this would be much appreciated !