Just installed Mate this morning and when I booted PC I was not able to log-in. Kept getting message that I was using wrong password. It seemed unlikely that I had made an error in typing the password during the install since your have to confirm password. But just in the unlikely event that I had made a typo, I decided to re-install Mate again, this time typing very carefully with only one finger. But results were the same when I tried to log-in. Is there anyway I can boot with a live DVD and change the log-in setup? I hate to have to do a third install! Next time I will choose automatic log-in!

maybe you used some special characters in your password, that change when using a different keymap/locale?
try using only "normal" letters (a-z,A-Z) and numbers.
maybe you can change the password by booting into recovery mode.
the command is:
where you should insert your username.