I am using Debian and I have recently tried to use the testing (wheezy) package. After I upgraded gcc, gdm3 was removed (I don't know why), but it was possible to install it again using
apt-get install gdm3
I did so, but now after startup I can see a login screen with a list of users. when I choose a username and type a password, I only see the desktop background and nothing on it. I also run an ssh server, and ssh -X works, but it is too slow.