[ubuntu] Ubuntu appereance problem

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http://ubuntuforums.org – My Ubuntu 12.04 was going good on PC. I am not an expert on Ubuntu. But the next day when i opened up my PC I found that the appearance of my ubuntu has been changed to something like basic or flat. I checked the theme setting but it was the default Ambiance theme. The network icon on the top toolbar was gone and there was only "User Folder Update" application on the default startup applications. Also there is no options for choosing "Ubuntu" and "Ubuntu 2D" on the logon screen. The theme is like the basic theme with grey color same as that of Windows xp. Please h (Hardware)