Changed monitor and am back running X after a dpkg-reconfigure xserver-xfree86.
Problem is the windows are way too big for the 1024 x 780 resolution, and the desktop does not fit into the screen.
X is started from GDM
If I startx -- -depth 24 as root it’s fine, just how it should be. Trying this from a normal user does not work, it’s the same result as logging in from GDM.
Depth 24 is the default in /etc/XF86Config.
Can someone point me to relevant doco about where to change this setting.