Problems with upgrade from Wheezy to Jessie

[Hans Kraus <hans@hanswkraus.com>]

Hi,

I upgraded my Debian server about a week ago from Wheezy to Jessie.
After that the GUI stopped, I see only  the grey screen with the sad
computer telling me " Oh no, Something is Wrong" and the only option is
to log out.

I'm using Gnome as my desktop. I installed the package again with:
apt-get install task-gnome-desktop
I did not get any error message, but that didn't cure my problem.

Afterwards I tried: "dpkg --configure -a". Again, I didn't get any
error message but  that didn't cure my problem.

I rebooted the system several times but with no avail.

Which info should I provide and/or where should I check my system for
errors? The text based login via ssh (I use Putty from Win 8.1)
functions without problems.

Kind regards, Hans