Ignore this post.
I discovered this thread and all working:
I have installed 12.12.1 64-bit on a DELL optiplex 755.
All seems to work perfectly after installing from the Live DVD. I then do:
After installing all updates I then reboot but after entering the login password the screen hangs with the login background and never gets to the desktop.
Mouse movement is OK and if I switch to a console it seems to function OK.