Installed Ubuntu on External HD but cant use it says I need a username and password

[Lex_15]

I used the passwords and usernames that I have on my computer and others that I use... Any suggestions or did I do something wrong it says that its incorrect username and password and that the password is case sensitive.. This is my first time using Ubuntu its the latest version

Thanks in Advance

[Lex_15]

Just installed and uninstalled and worked.