I am using using ubuntu 11.10. Everything was working perfectly this morning. At a moment "Ubuntu software center" application was unable to get started. So I restarted by system and when I logged in it started under GNOME. Again when I try to start in ubuntu session then it was not showing in menu list but Ubuntu 2D is coming. I don't come to know why this is happening. please let me know any fix for this issue. Thanks!