Fresh Ubuntu 24.04 installation has failed four times

Question

Folks, After using Ubuntu LTSs for around fifteen years I have just encountered a failure in my 22.04 version; I decided to move to the latest version, rather than try to fix the problem I was having. I downloaded and installed 24.04, full of confidence, hope and optimism. I've never before had any issue with any Ubuntu installation. I have the /Home folder on a separate partition and it has always worked well for me, obviating the need to reinstall personal folders. In the install procedure I unticked the box asking whether I wanted to login each time I turned the machine on, while reusing the same old username and password that I've been using for those fifteen years. Alas, the machine still asks me to log in (even though that box was unticked) and, even though I use my normal username and password, I still cannot make any headway with this machine. I've been through the process five times but the result is always the same. When I finally decided to turn the machine off, I received a message that there were "other users still logged in". I am the only user of this machine (same username and password). Can anyone suggest what might be causing this problem? It's tremendously frustrating. Thanks