Welcome to the Community,
do you have any special characters in the password, which may be on different keys depending on the keyboard layout (language)?
Such issues often occur when the correct keyboard layout is not selected during installation.
Btw. how did you enable Shell access without access to the DCUI, or the GUI?
Try the below and check if the account is locked
if its shows locked then unlock the account using
Pam_tally2 --user=root --reset