Recently i installed compiz configuration manager after that i went to unity under that and clicked "reset to defaults". This caused the dock bar to disappear and also close maximize and minimize buttons have dissapeared for all windows.I am running ubuntu 12.04 LTS. It will be really helpful if some one can help me solve this issue.
Press Ctrl + Alt + F1 to access a command line only session, login with your usual username and password, and run the command
unity --reset to reset all your Unity related settings. You can then get back to the usual graphical session by pressing Ctrl + Alt + F7.