Back to the login screen immediately after login

After login the the default gnome desktop, there is nothing but only в background picture. Then after во вспышку of в black screen, it returns back to the login интерфейс.

I changed to tty1 by Ctrl+Alt+F1. By typing startx I хан log into gnome with icons on the desktop but without gnome панель. I added mutter and gnome-panel into the Стартуп Аппликатионс so that I don't have to run them in the терминал every украл. Then I хан использовал this gnome environment общепринятый туз.

But change back to the default desktop by Ctrl+Alt+F7, I still cannot login.

To sum up, I cannot login the default gnome, but хан login the gnome started by startx.