root password not accepted

[Albert DE WINT <adwint pandora be>]

Hello,

Today I installed Redhat 9 twice, yes, twice.
 
After the first trial, it refused my root password.
I guessed I had made a mistake, so I did the installation all over
again.

To my surprise it still does not accept my root password after the
second trial. So, I can't run updates, can't add users, can't make any
essential modification.

I am 100% sure I did not make a mistake; I must have used this password
at least 1000 times.

I hope there is no connection to my nVIDIA Geforce MX card.
I noticed sometimes little parts in the screen break-up.
I'd like to install the nVidia 3D driver, obviously I need to do that as
root.

Any ideas?

Albert