Parallel

Can you access the GUI? Open System Settings>User Accounts. There should be a list of users on the left with a display name in bold and the username underneath in non-bold. If you can't access the GUI, I'm not sure if you can check for usernames. Try guessing random usernames. Also, I believe usernames have to be lowercase? Don't quote me on that, but if you were trying with capitals previously, try an all-lowercase username.