Thank you so much everyone for your help.
I finally managed to log in and after trying a few things, I was convinced that Ooo had caused the problem because it was working before I tried to install it . After this wonderful opportunity to work at the command line I got access to the Ooo file I previously tried to install and deleted it.
I restarted the computer and Oh surprise the log in screen appeared again without the need to correct anything in the display. The problem was that my disk was full... I have learnt a lesson then!
Now I would like to delete a few things to regain space (I am on a laptop Toshiba Satellite 2210, 6GB, 1/2 for Windows and 1/2 for Linux):
1. How to completely remove KDE application? I installed it with RedHat 8 and the upgrade to RedHat 9 kept it. In the package manager, KDE is not checked but I have it. Just like if the Manager has nothing to do with the new Redhat 9...
2. How would it be possible to reduce Windows partitiuon to 1/3 without messing around?
Concerning the display I have occasionaly some dirty lines appearing (on laptop and external monitor) that can be swept out with the mouse.. what can I do to correc this.
Than you once again.