Somehow my client an me messed it up with the user password.
After some time I found out how to reset the root user password.
However the process is not working with the normal user.
When login screen loads the user box shows up but shows login error after providing the user password.
This user password has been configured using the same GRUB menu.
Another thing, once in as root, I cannot see the user folder.
When you logged in as root the user folder of root points in the file system to /root
All other users except root have their home in /home/username
Now as you have root access you can try to change the users password in the terminal like:
passwd username and following the dialogue.
If this not works, you messed something up. To find this out you might give us a bit more information what exactly you made so far.